# conversion of units

Conversion of units refers to conversion factors between different units of measurement for the same quantity. |

## Techniques

The simplest way to convert from one unit to another is to carry through the units themselves in the mathematical operation. To illustrate this process, consider the following examples.

Suppose one wishes to convert 6 feet into metres. Consulting the table below and finding that one foot is exactly 0.3048 metre, one can now perform the mathematical conversion:
6 ft × 0.3048 m/ft = 1.8288 m
Notice that the "foot" units canceled out, leaving only metres, the desired result. (Since 0.3048 metre per foot have infinite precision, the precision of the answer is determined by the precision of the 6 ft figure; if, for example, you are defining the fathom, expressing it with 5 significant figures is correct. But if the 6 ft figure is a measurement, the result needs to be rounded appropriately.)

Say a person's height is 183 centimetres, and one wishes to convert this into inches:
183 cm / (2.54 cm/in) = 72.0 in

To check the answer, the result can be converted back into feet:
72 in / (12 in/ft) = 6.0 feet
which confirms the earlier result.

Multiple units can be manipulated in the same fashion:
7 mi/s × 1.609344 km/mi × 3600 s/h = 40,000 km/h

Thus, Earth's escape velocity is about 7 miles per second, or 40,000 kilometres per hour. Notice that since the calculation started with one significant figure (the 7), the answer also has one significant figure (the 4 in 40,000).

Deciding whether to multiply or divide is determined by looking at the units and deciding which ones it is desired to "get rid" of. In the conversion just above, if one had divided by 3600 s/h instead of multiplying, the result would have come out in kilometre-hours per square second, clearly an incorrect and meaningless result.

Why does it work? Notice that because the numerator and denominator describe the same quantity, the factor is equivalent to the number 1. Therefore, multiplication by this factor does not change the measured quantity, only its units.

## Rounding of results

An important thing to remember is that the process of making a conversion cannot produce a more precise result than that with which one started. While many of the conversion factors given in the tables below are exact, and others, while not exact, contain many significant digits, not all the numbers resulting from performing calculations on a calculator or with pencil and paper are meaningful.

After using these conversion factors, be sure to round off the results appropriately. See significant figures for more details on rounding correctly.

## Tables of conversion factors

### Legend

= definition exactly equal to approximately equal to indicates the digits repeat infinitely

### Length

Length, l
Name of unit Symbol Definition Relation to SI units
ångströmÅ≡ 110−10 m = 0.1 nm
astronomical unitAUMean distance from Earth to the Sun= 149 597 870.691 ± 0.030 km
atomic unit of lengthau≡ a0≈ 5.291 772 08310−11 ± 1910−20 m
barley corn ≡ 1/3 in≈ 8.466 667 mm
Bohr radiusa0; bα/(4πR)≈ 5.291 772 08310−11 ± 1910−20 m
cable length (Imperial) ≡ 608 ft= 185.3184 m
cable length (International) ≡ 1/10 NM= 185.2 m
cable length (U.S.) ≡ 720 ft= 219.456 m
calibrecal≡ 1 in= 25.4 mm
chain (Gunter's; Surveyor's)ch≡ 66.0 ft (4 rods)= 20.1168 m
chain (Ramsden's; Engineer's)ch≡ 100 ft= 30.48 m
cubit ≡ 18 in= 0.4572 m
ellell≡ 45 in= 1.143 m
fathomfm≡ 6 ft= 1.8288 m
≈ 1/1000 NM= 1.852 m
fermifm≡ 110−15 m= 110−15 m
finger ≡ 7/8 in= 22.225 mm
finger (cloth) ≡ 4 ½ in= 0.1143 m
foot (Benoît)ft (Ben)≈ 0.304 799 735 m
foot (Clarke's; Cape)ft (Cla)≈ 0.304 797 265 4 m
foot (Indian)ft Ind≈ 0.304 799 514 m
foot (International)ft≡ 1/3 yd= 0.3048 m
foot (Sear's)ft (Sear)≈ 0.304 799 47 m
foot (U.S. Survey)ft (US)≡ 1200/3937 m [1]≈ 0.304 800 610 m
furlongfur≡ 660 ft (10 chains)= 201.168 m
geographical milemi≡ 6082 ft= 1853.7936 m
hand ≡ 4 in= 0.1016 m
inchin≡ 1/36 yd= 25.4 mm
leaguelea≡ 3 mi= 4828.032 m
light-day ≡ 24 light-hours= 2.590 206 837 121013 m
light-hour ≡ 60 light-minutes= 1.079 252 848 81012 m
light-minute ≡ 60 light-seconds= 1.798 754 7481010 m
light-second ≡ 2.997 924 58108 m
light-yearl.y.c0 × 86 400 × 365.25= 9.460 730 472 580 81015 m
lineln≡ 1/12 in (Klein 1988, 63)≈ 2.116 667 mm
link (Gunter's; Surveyor's)lnk≡ 1/100 ch= 0.201 168 m
link (Ramsden's; Engineer's)lnk≡ 1 ft= 0.3048 m
metre (SI base unit)m≡ 1 m= 1 m
mickey ≡ 1/200 in= 1.2710−4 m
micronµ≡ 1.00010−6 m
mil; thoumil≡ 1.00010−3 in= 2.5410−5 m
mil (Sweden and Norway)mil≡ 10 km= 10000 m
milemi≡ 1760 yd = 5280 ft= 1609.344 m
mile (U.S. Survey)mi≡ 5280 ft (US)= 5280 × 1200/3937 m ≈ 1609.347 219 m
nail (cloth) ≡ 2 ¼ in= 57.15 mm
nautical leagueNL; nl≡ 3 NM= 5556 m
nautical mileNM; nmi≡ 1852 m≡ 1852 m
pace ≡ 2.5 ft= 0.762 m
palm ≡ 3 in= 76.2 mm
parsecpc≈ 180 × 60 × 60/π AU
= 206264.8062 AU
= 3.26156378 light-years
= 3.08567782 1016 ± 6106 m [2]
point (ATA)pt≡ 0.013837 in= 0.351 459 8 mm
point (Didot; European)pt≡ 0.376 065 mm
point (metric)pt≡ 3/8 mm= 0.375 mm
point (PostScript)pt≡ 1/72 in≈ 0.352 778 mm
quarter ≡ ¼ yd= 0.2286 m
rod; pole; perchrd≡ 16 ½ ft= 5.0292 m
roperope≡ 20 ft= 6.096 m
span ≡ 6 in= 0.1524 m
span (cloth) ≡ 9 in= 0.2286 m
spat[1]≡ 1012 m= 1 Tm
stick ≡ 2 in= 50.8 mm
stigma; pm ≡ 1.00010−12 m≡ 1.00010−12 m
telegraph milemi≡ 6087 ft= 1855.3176 m
twiptwp≡ 1/1440 in≈ 1.763 88910−5 m
x unit; siegbahnxu≈ 1.002110−13 m
yard (International)yd≡3 ft ≡ 0.9144 m [1]= 0.9144 m

### Area

Area, A
Name of unit Symbol Definition Relation to SI units
acreac≡ 10 sq ch = 4840 sq yd= 4046.856 422 4 m²
area≡ 100 m²
barnb≡ 10−28
barony ≡ 4000 ac= 1.618 742 568 96107
boardbd≡ 1 in × 1 ft= 7.741 9210−3
boiler horsepower equivalent direct radiationbhp EDR≡ (1 ft²) (1 bhp) / (240 BTUIT/h)≈ 12.958 174 m²
circular inchcirc in≡ π/4 in²≈ 5.067 07510−4
circular mil; circular thoucirc mil≡ π/4 mil²≈ 5.067 07510−10
cord ≡ 192 bd= 1.486 448 64 m²
dunam ≡ 1000 m²= 1000 m²
hectareha≡ 10 000 m²= 0.01 km²
hide ≡ 100 ac= 4.046 856 422 4105
roodro≡ ¼ ac= 1011.714 105 6 m²
square chainsq ch≡ 1 ch²= 404.685 642 24 m²
square footsq ft≡ 1 ft²= 9.290 30410−2
square inchsq in≡ 1 in²= 6.451610−4
square kilometrekm²≡ 1 km²= 106
square linksq lnk≡ 1 lnk²= 4.046 856 422 410−2
square metre (SI unit)≡ 1 m × 1 m= 1 m²
square mil; square thousq mil≡ 1 mil²= 6.451610−10
square mile; sectionsq mi≡ 1 mi²= 2.589 988 110 336106
square rod/pole/perchsq rd≡ 1 rd²= 25.292 852 64 m²
square U.S. Survey footsq ft≡ 1 ft (US)²≈ 9.290 341 161 327 4910-2
square U.S. Survey milesq mi≡ 1 mi (US)²≈ 2.589 998106
square yardsq yd≡ 1 yd²= 0.836 127 36 m²
stremma ≡ 1000 m²= 1000 m²
township ≡ 36 sq mi (US)≈ 9.323 994107
yardland ≡ 30 ac= 1.214 056 926 72105

### Volume

Volume, V
Name of unit Symbol Definition Relation to SI units
cubic metre (SI unit)≡ 1 m × 1 m × 1 m
litreL≡ 1 dm³
lambda?≡ 1 mm³= 1 μL
drop (metric) ≡ 1/20 mL= 0.05 mL
minim (Imperial)min≡ 1/480 fl oz (Imp) = 1/60 fl dr (Imp)≈ 0.059 193 880 208 333 mL
minim (U.S.)min≡ 1/480 US fl oz = 1/60 US fl dr= 0.061 611 519 921 875 mL
drop (U.S.) (alt)gtt≡ 1/456 US fl oz≈ 0.064 854 231 mL
drop (Imperial) (alt)gtt≡ 1/1824 gi (Imp)≈ 0.077 886 684 mL
drop (U.S.)gtt≡ 1/360 US fl oz= 0.082 148 693 229 1(6) mL
drop (medical) ≡ 1/12 mL= 0.08(3) mL
drop (Imperial)gtt≡ 1/288 fl oz (Imp)= 0.098 656 467 013 (8) mL
dash (U.S.) ≡ 1/96 US fl oz = ½ US pinch= 0.308 057 599 609 375 mL
dash (Imperial) ≡ 1/384 gi (Imp) = ½ pinch (Imp)= 0.369 961 751 302 08(3) mL
pinch (U.S.) ≡ 1/48 US fl oz = ⅛ US tsp= 0.616 115 199 218 75 mL
pinch (Imperial) ≡ 1/192 gi (Imp) = ⅛ tsp (Imp)= 0.739 923 502 604 1(6) mL
fluid scruple (Imperial)fl s≡ 1/24 fl oz (Imp)= 1.183 877 604 1(6) mL
fluid drachm (Imperial)fl dr≡ ⅛ fl oz (Imp)= 3.551 632 812 5 mL
fluid dram (U.S.); U.S. fluidramfl dr≡ ⅛ US fl oz= 3.696 691 195 312 5 mL
teaspoon (Canadian)tsp≡ 1/6 fl oz (Imp)≈ 4.735 510 416 667 mL
teaspoon (U.S.)tsp≡ 1/6 US fl oz= 4.928 921 595 mL
teaspoon (metric) ≡ 5 mL
teaspoon (Imperial)tsp≡ 1/24 gi (Imp)= 5.919 388 020 8(3) mL
dessertspoon (Imperial) ≡ 1/12 gi (Imp)= 11.838 776 041 (6) mL
tablespoon (Canadian)tbsp≡ ½ fl oz (Imp)= 14.206 531 25 mL
tablespoon (U.S.)tbsp≡ ½ US fl oz= 14.786 764 782 5 mL
tablespoon (metric) ≡ 15 mL
cubic inchcu in≡ 1 in³= 16.387 064 mL
tablespoon (Imperial)tbsp≡ 5/8 fl oz (Imp)= 17.758 164 062 5 mL
pony ≡ 3/4 US fl oz= 22.180 147 171 875 mL
fluid ounce (Imperial)fl oz (Imp)≡ 1/160 gal (Imp)= 28.413 062 5 mL
fluid ounce (U.S.)fl oz (US)≡ 1/128 gal (US)= 29.573 529 562 5 mL
shot ≡ 1 US fl oz= 29.573 529 562 5 mL
jigger ≡ 1½ US fl oz= 44.360 294 343 75 mL
gill (U.S.)gi (US)≡ 4 US fl oz= 118.294 118 25 mL
gill (Imperial); Noggingi (Imp); nog≡ 5 fl oz (Imp)= 142.065 312 5 mL
cup (Canadian)c (CA)≡ 8 fl oz (Imp)= 227.3045 mL
cup (U.S.)c (US)≡ 8 US fl oz ≡ 1/16 gal (US)= 236.588 236 5 mL
cup (metric)c≡ 250 mL
breakfast cup ≡ 10 fl oz (Imp)= 284.130 625 mL
pint (U.S. fluid)pt (US fl)≡ ⅛ gal (US)= 473.176 473 mL
pint (U.S. dry)pt (US dry)≡ 1/64 bu (US lvl) ≡ ⅛ gal (US dry)= 0.550 610 471 357 5 L
pint (Imperial)pt (Imp)≡ ⅛ gal (Imp)= 0.568 261 25 L
fifth ≡ 1/5 US gal= 0.757 082 356 8 L
quart (U.S. fluid)qt (US)≡ ¼ gal (US fl)= 0.946 352 946 L
quart (U.S. dry)qt (US)≡ 1/32 bu (US lvl) = ¼ gal (US dry)= 1.101 220 942 715 L
quart (Imperial)qt (Imp)≡ ¼ gal (Imp)= 1.136 522 5 L
pottle; quartern ≡ ½ gal (Imp) = 80 fl oz (Imp)= 2.273 045 L
board-footfbm≡ 144 cu in= 2.359 737 216 L
gallon (U.S. fluid; Wine)gal (US)≡ 231 cu in= 3.785 411 784 L
gallon (U.S. dry)gal (US)≡ ⅛ bu (US lvl)= 4.404 883 770 86 L
gallon (Imperial)gal (Imp)== 4.546 09 L
beer gallonbeer gal≡ 282 cu in= 4.621 152 048 L
peck (U.S. dry)pk≡ ¼ US lvl bu= 8.809 767 541 72 L
peck (Imperial)pk≡ 2 gal (Imp)= 9.092 18 L
bucket (Imperial)bkt≡ 4 gal (Imp)= 18.184 36 L
timber foot ≡ 1 cu ft= 28.316 846 592 L
cubic footcu ft≡ 1 ft × 1 ft × 1 ft= 28.316 846 592 L
firkin ≡ 9 gal (US)= 34.068 706 056 L
bushel (U.S. dry level)bu (US lvl)≡ 2150.42 cu in= 35.239 070 166 88 L
bushel (Imperial)bu (Imp)≡ 8 gal (Imp)= 36.368 72 L
bushel (U.S. dry heaped)bu (US)≡ 1 ¼ bu (US lvl)= 44.048 837 708 6 L
strike (U.S.) ≡ 2 bu (US lvl)= 70.478 140 333 76 L
strike (Imperial) ≡ 2 bu (Imp)= 72.737 44 L
kilderkin ≡ 18 gal (Imp)= 81.829 62 L
sack (U.S.) ≡ 3 bu (US lvl)= 105.717 210 500 64 L
sack (Imperial); bag ≡ 3 bu (Imp)= 109.106 16 L
barrel (U.S. dry)bl (US)≡ 105 qt (US) = 105/32 bu (US lvl)= 115.628 198 985 075 L
barrel (U.S. fluid)fl bl (US)≡ 31½ gal (US)= 119.240 471 196 L
coomb ≡ 4 bu (Imp)= 145.474 88 L
barrel (petroleum)bl≡ 42 gal (US)= 158.987 294 928 L
barrel (Imperial)bl (Imp)≡ 36 gal (Imp)= 163.659 24 L
hogshead (U.S.)hhd (US)≡ 2 fl bl (US)= 238.480 942 392 L
seam ≡ 8 bu (US lvl)= 281.912 561 335 04 L
quarter; pail ≡ 8 bu (Imp)= 290.949 76 L
hogshead (Imperial)hhd (Imp)≡ 2 bl (Imp)= 327.318 48 L
cord-foot ≡ 16 cu ft= 0.453 069 545 472 m³
butt, pipe ≡ 126 gal (wine)= 0.476 961 884 784 m³
perchper≡ 16½ ft × 1½ ft × 1 ft= 0.700 841 953 152 m³
cubic yardcu yd≡ 27 cu ft= 0.764 554 857 984 m³
tun ≡ 252 gal (wine)= 0.953 923 769 568 m³
displacement ton ≡ 35 cu ft= 0.991 089 630 72 m³
water ton ≡ 28 bu (Imp)= 1.018 324 16 m³
freight ton ≡ 40 cu ft= 1.132 673 863 68 m³
wey (U.S.) ≡ 40 bu (US lvl)= 1.409 562 806 675 2 m³
load ≡ 50 cu ft= 1.415 842 329 6 m³
register ton ≡ 100 cu ft= 2.831 684 659 2 m³
last ≡ 80 bu (Imp)= 2.909 497 6 m³
cord (firewood) ≡ 8 ft × 4 ft × 4 ft= 3.624 556 363 776 m³
cubic fathomcu fm≡ 1 fm × 1 fm × 1 fm= 6.116 438 863 872 m³
acre-inch ≡ 1 ac × 1 in= 102.790 153 128 96 m³
acre-foot ≡ 1 ac × 1 ft= 1233.481 837 547 52 m³
cubic milecu mi≡ 1 mi³= 4.168 181 825 440 579 584 km³

### Angle

Angle
Name of unit Symbol Definition Relation to SI units
centesimal second of arc"≡ 1 gr/10000≈ 1.570 796 µrad
centesimal minute of arc'≡ 1 gr/100≈ 0.157 080 mrad
minute of arc'≡ 1°/60≈ 0.290 888 mrad
sign ≡ 30°≈ 0.523 599 rad
octant ≡ 45°≈ 0.785 398 rad
sextant ≡ 60°≈ 1.047 198 rad

### Solid angle

Solid angle
Name of unit Symbol Definition Relation to SI units

### Mass

Note: see Weight for detail of mass/weight distinction and conversion
Mass, m
Name of unit Symbol Definition Relation to SI units Relation to avoirdupois units
kilogram, gravekg; G(SI base unit)
electron rest massme≈ 9.109 381 8810−31 ± 7210−39 kg
atomic unit of massau≡ me≈ 9.109 381 8810−31 ± 7210−39 kg
unified atomic mass unitu≈ 1.660 538 7310−27 ± 1310−35 kg
daltonDa≈ 1.660 902 1010−27 ± 1310−35 kg
gamma?≡ 1 μg
point ≡ 1/100 kt (metric)= 2 mg
mite ≡ 1/20 gr= 3.239 945 5 mg
mite (metric) ≡ 1/20 g= 50 mg
graingr≡ 64.798 91 mg
crith ≈ 89.9349 mg
carat (metric)kt≡ 200 mg
caratkt≡ 3 1/6 gr≈ 205.196 548 333 mg
sheet ≡ 1/700 lb av= 647.9891 mg
scruple (avoirdupois)s av≡ 20 gr= 1.295 978 2 g
pennyweightdwt; pwt≡ 1/20 oz t= 1.555 173 84 g
dram (avoirdupois)dr av≡ 27 11/32 gr= 1.771 845 195 312 5 g
dram (apothecary; troy)dr t≡ 60 gr= 3.887 934 6 g
hyl (CGS unit) ≡ 1 gee × 1 g × 1 s²/m= 9.806 65 g
ounce (avoirdupois)oz av≡ 1/16 lb= 28.349 523 125 g
assay ton (short)AT≡ 1 mg × 1 sh tn ÷ 1 oz t≈ 29.166 667 g
ounce (apothecary; troy)oz t≡ 1/12 lb t= 31.103 476 8 g
assay ton (long)AT≡ 1 mg × 1 long tn ÷ 1 oz t≈ 32.666 667 g
mark ≡ 8 oz t= 248.827 814 4 g
pound (troy)lb t≡ 5760 grains= 0.373 241 721 6 kg
pound (avoirdupois)lb av≡ 7000 grains= 0.453 592 37 kg
pound (metric) ≡ 500 g
clove ≡ 8 lb av= 3.628 738 96 kg
stonest≡ 14 lb av= 6.350 293 18 kg
hyl (MKS unit) ≡ 1 gee × 1 kg × 1 s²/m= 9.806 65 kg
quarter (Imperial) ≡ 1/4 long cwt = 2 st = 28 lb av= 12.700 586 36 kg
slug; geepoundslug≡ 1 gee × 1 lb av × 1 s²/ft≈ 14.593 903 kg
bag (Portland cement) ≡ 94 lb av= 42.637 682 78 kg
short hundredweight; centalsh cwt≡ 100 lb av= 45.359 237 kg
long hundredweightlong cwt or cwt≡ 112 lb av= 50.802 345 44 kg
bag (coffee)≡ 60 kg= 60 kg
quintal (metric)q≡ 100 kg
wey ≡ 252 lb = 18 st= 114.305 277 24 kg (variants exist)
long quarter ≡ ¼ long tn= 254.011 727 2 kg
kipkip≡ 1000 lb av= 453.592 37 kg
short tonsh tn≡ 2000 lb= 907.184 74 kg
tonne (mts unit)t≡ 1000 kg
long tonlong tn or ton≡ 2240 lb= 1016.046 908 8 kg
barge ≡ 22 ½ sh tn= 20,411.656 65 kg
In physics, the pound of mass is sometimes written lbm to distinguish it from the pound-force (lbf). It should not be read as the mongrel unit "pound metre".

### Time

Time, t
Name of unit Symbol Definition Relation to SI units
seconds(SI base unit)
Planck time ≡ √(Gℏ/c5)≈ 1.351 211 81810−43 s
atomic unit of timeaua0/(α·c)≈ 2.418 884 25410−17 s
svedbergS≡ 10−13 s= 100 fs
shake ≡ 10−8 s= 10 ns
sigma ≡ 10−6 s= 1 μs
jiffy ≡ 1/60 s≈ 16.666 667 ms
jiffy (alternate) ≡ 1/100 s= 10 ms
helek ≡ 1/1080 h≈ 3.333333 s
minutemin≡ 60 s
millidaymd≡ 86 400 s / 1000≡ 86.4 s
moment ≡ 90 s≡ 90 s
ke(traditional) ≡ 1/100 d≡ 864 s
quarter (of an hour)ke≡ 1/96 d≡ 900 s
hourh≡ 60 min= 3600 s
dayd≡ 24 h= 86 400 s
weekwk≡ 7 d= 604 800 s
fortnight ≡ 2 wk= 1 209 600 s
month (hollow)mo≡ 29 d= 2 505 600 s
monthmo≡ 30 d= 2 592 000 s
month (full)mo≡ 31 d= 2 678 400 s
year (Calendar)a or y≡ 365 d= 31 536 000 s
year (Gregorian)a or y≡ 365.2425 d= 31 556 952 s
year (Julian)a or y≡ 365.25 d= 31 557 600 s
sidereal yeara or y≡ 365.256363 d= 31 558 149.76 s
Olympiad ≡ 4 a of 365 d= 1.2614108 s
lustre; lustrum ≡ 5 a of 365 d= 1.5768108 s
octaeteris ≡ 8 a of 365 d= 2.522 88108 s
decade ≡ 10 a of 365 d= 3.1536108 s
enneadecaeteris; Metonic cycle ≡ 110 mo (hollow) + 125 mo (full) = 19 a of 365 d= 5.996 16108 s
Callippic cycle ≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d= 2.398 377 6109 s
century (Calendar) ≡ 100 a of 365 d= 3.1536109 s
century (Julian) ≡ 100 a of 365.25 d= 3.155 76109 s
Hipparchic cycle ≡ 4 Callippic cycles - 1 d= 9.593 424109 s
millennium (Calendar) ≡ 1000 a of 365 d= 3.15361010 s
millennium (Gregorian) ≡ 1000 a of 365.2425 d= 3.155 695 21010 s
millennium (Julian) ≡ 1000 a of 365.25 d= 3.155 761010 s
Sothic cycle ≡ 1461 a of 365 d= 4.607 409 61010 s

### Speed

Speed, v
Name of unit Symbol Definition Relation to SI units
metre per second (SI unit)m/s≡ 1 m/s
foot per hourfph≡ 1 ft/h≈ 8.466 66710−5 m/s
furlong per fortnight ≡ ½ fur/wk≈ 1.663 09510−4 m/s
inch per minuteipm≡ 1 in/min≈ 4.23 33310−4 m/s
foot per minutefpm≡ 1 ft/min= 5.0810−3 m/s
inch per secondips≡ 1 in/s= 2.5410−2 m/s
kilometre per hourkm/h≡ 1 km/h≈ 2.777 77810−1 m/s
foot per secondfps≡ 1 ft/s= 3.04810−1 m/s
mile per hourmph≡ 1 mi/h= 0.447 04 m/s
knotkn≡ 1 NM/h = 1.852 km/h≈ 0.514 444 m/s
knot (Admiralty)kn≡ 1 NM (Adm)/h = 1.853 184 km/h≈ 0.514 773 m/s
mile per minutempm≡ 1 mi/min= 26.8224 m/s
mile per secondmps≡ 1 mi/s= 1.609 344 km/s
speed of light in vacuumc≡ 2.997 924 58108 m/s

### Acceleration

Acceleration, a
Name of unit Symbol Definition Relation to SI units
metre per second squared (SI unit)m/s²≡ 1 m/s²
foot per hour per secondfph/s≡ 1 ft/(h·s)≈ 8.466 66710−5 m/s²
inch per minute per secondipm/s≡ 1 in/(min·s)≈ 4.233 33310−4 m/s²
foot per minute per secondfpm/s≡ 1 ft/(min·s)= 5.0810−3 m/s²
galileoGal≡ 1 cm/s²= 10−2 m/s²
inch per second squaredips²≡ 1 in/s²= 2.5410−2 m/s²
foot per second squaredfps²≡ 1 ft/s²= 3.04810−1 m/s²
mile per hour per secondmph/s≡ 1 mi/(h·s)= 4.470410−1 m/s²
knot per secondkn/s≡ 1 kn/s≈ 5.144 44410−1 m/s²
standard gravityg≡ 9.806 65 m/s²
mile per minute per secondmpm/s≡ 1 mi/(min·s)= 26.8224 m/s²
mile per second squaredmps²≡ 1 mi/s²= 1.609 344103 m/s²

### Force

Force, F
Name of unit Symbol Definition Relation to SI units
newton (SI unit)N≡ kg·m/s²
atomic unit of forceau≡ me·α²·c²/a0≈ 8.238 722 24110−8 N
dyne (cgs unit)dyn≡ g·cm/s²ljm = 10−5 N
milligrave-force, gravet-forcemGf; gfg × 1 g= 9.806 65 mN
poundalpdl≡ 1 lb·ft/s²= 0.138 254 954 376 N
ounce-forceozfg × 1 oz= 0.278 013 850 953 781 2 N
pound-forcelbfg × 1 lb= 4.448 221 615 260 5 N
kilogram-force; kilopond; grave-forcekgf; kp; Gfg × 1 kg= 9.806 65 N
sthene (mts unit)sn≡ 1 t·m/s²= 1 kN
kip; kip-forcekip; kipf; klbfg × 1000 lb= 4.448 221 615 260 5 kN
ton-forcetnfg × 1 sh tn= 8.896 443 230 521 kN

### Pressure or mechanical stress

Pressure, p (lower case)
Name of unit Symbol Definition Relation to SI units
atmosphere (standard)atm≡ 101 325 Pa [5]
atmosphere (technical)atm≡ 1 kgf/cm²= 98.0665 kPa [5]
barbar≡ 105 Pa
barye (cgs unit) ≡ 1 dyn/cm²= 0.1 Pa
centimetre of mercurycmHg≡ 13 595.1 kg/m³ × 1 cm × g≈ 1.333 22 kPa [5]
centimetre of water (4 °C)cmH2O≈ 999.972 kg/m³ × 1 cm × g≈ 98.0638 Pa [5]
foot of mercury (conventional)ftHg≡ 13 595.1 kg/m³ × 1 ft × g≈ 40.636 66 kPa [5]
foot of water (39.2 °F)ftH2O≈ 999.972 kg/m³ × 1 ft × g≈ 2.988 98 kPa [5]
inch of mercury (conventional)inHg≡ 13 595.1 kg/m³ × 1 in × g≈ 3.386 389 kPa [5]
inch of water (39.2 °F)inH2O≈ 999.972 kg/m³ × 1 in × g≈ 249.082 Pa [5]
kilogram-force per square millimetrekgf/mm²≡ 1 kgf/mm²= 9.806 65 MPa [5]
kip per square inchksi≡ 1 kipf/sq in≈ 6.894757 MPa [5]
millimetre of mercurymmHg≡ 13 595.1 kg/m³ × 1 mm × g ≈ 1 torr≈ 133.322 4 Pa [5]
millimetre of water (3.98 °C)mmH2O≈ 999.972 kg/m³ × 1 mm × g= 9.806 38 Pa (= 0.999972 kgf/m²)
pascal (SI unit)Pa≡ N/m²= kg/(m·s²) [6]
pièze (mts unit)pz≡ 1000 kg/m·s²= 1 kPa
pound per square footpsf≡ 1 lbf/ft²≈ 47.880 25 Pa [5]
poundal per square footpdl/sq ft≡ 1 pdl/sq ft≈ 1.488 164 Pa [5]
pound per square inchpsi≡ 1 lbf/in²≈ 6.894 757 kPa [5]
short ton per square foot ≡ 1 sh tn × g / 1 sq ft≈ 95.760 518 kPa
torrtorr≡ 101 325/760 Pa≈ 133.322 4 Pa [5]

### Energy, work, or heat

Energy, E
Name of unit Symbol Definition Relation to SI units
joule (SI unit)J≡ N·m = W·s = V·A·s= kg·m²/s²
electronvolteVe × 1 V≈ 1.602 17610−19 J
rydbergRyR··c≈ 2.179 87210−18 J
hartreeEh≡ me·α²·c² (= 2 Ry)≈ 4.359 74410−18 J
atomic unit of energyau≡ Eh≈ 4.359 74410−18 J
erg (cgs unit)erg≡ 1 g·cm²/s²= 10−7 J
foot-poundalft pdl≡ 1 lb·ft²/s²= 4.214 011 009 380 4810−2 J
cubic centimetre of atmosphere; standard cubic centimetrecc atm; scc≡ 1 atm × 1 cm³= 0.101 325 J
inch-pound forcein lbfg × 1 lb × 1 in= 0.112 984 829 027 616 7 J
Foot-pound forceft lbfg × 1 lb × 1 ft= 1.355 817 948 331 400 4 J
calorie (20 °C)cal20 °C≈ 4.1819 J
calorie (thermochemical)calth≡ 4.184 J
calorie (15 °C)cal15 °C≡ 4.1855 J
calorie (International Table)calIT≡ 4.1868 J
calorie (mean)calmean≈ 4.190 02 J
calorie (3.98 °C)cal3.98 °C≈ 4.2045 J
litre-atmospherel atm; sl≡ 1 atm × 1 L= 101.325 J
gallon-atmosphere (U.S.)US gal atm≡ 1 atm × 1 gal (US)= 383.556 849 013 8 J
gallon-atmosphere (Imperial)US gal atm≡ 1 atm × 1 gal (Imp)= 460.632 569 25 J
British thermal unit (thermochemical)BTUth≡ 1 lb/g × 1 calth × 1 °F/°C = 9.489 152 380 4 ÷ 9 kJ≈ 1.054 350 kJ
British thermal unit (ISO)BTUISO≡ 1.0545 kJ
British thermal unit (63 °F)BTU63 °F≈ 1.0546 kJ
British thermal unit (60 °F)BTU60 °F≈ 1.054 68 kJ
British thermal unit (59 °F)BTU59 °F≡ 1.054 804 kJ
British thermal unit (International Table)BTUIT≡ 1 lb/g × 1 calIT × 1 °F/°C= 1.055 055 852 62 kJ
British thermal unit (mean)BTUmean≈ 1.055 87 kJ
British thermal unit (39 °F)BTU39 °F≈ 1.059 67 kJ
Celsius heat unit (International Table)CHUIT≡ 1 BTUIT × 1 °C/°F= 1.899 100 534 716 kJ
cubic foot of atmosphere; standard cubic footcu ft atm; scf≡ 1 atm × 1 ft³= 2.869 204 480 934 4 kJ
kilocalorie; large caloriekcal; Cal≡ 1000 calIT= 4.1868 kJ
cubic yard of atmosphere; standard cubic yardcu yd atm; scy≡ 1 atm × 1 yd³= 77.468 520 985 228 8 kJ
cubic foot of natural gas ≡ 1000 BTUIT= 1.055 055 852 62 MJ
horsepower-hourhp·h≡ 1 hp × 1 h= 2.6845 MJ
kilowatt-hour; Board of Trade UnitkW·h; B.O.T.U.≡ 1 kW × 1 h= 3.6 MJ
thermieth≡ 1 McalIT= 4.1868 MJ
therm (U.S.) ≡ 100 000 BTU59 °F= 105.4804 MJ
therm (E.C.) ≡ 100 000 BTUIT= 105.505 585 262 MJ
ton of TNTtTNT≡ 1 Gcalth= 4.184 GJ
barrel of oil equivalentbboe≈ 5.8 MBTU59 °F≈ 6.12 GJ
ton of coal equivalentTCE≡ 7 Gcalth= 29.3076 GJ
ton of oil equivalentTOE≡ 10 Gcalth= 41.868 GJ
quad ≡ 1015 BTUIT= 1.055 055 852 62 EJ

### Power

Power, P
Name of unit Symbol Definition Relation to SI units
watt (SI unit)W≡ J/s = N·m/s= kg·m²/s³
luseclusec≡ 1 L·µmHg/s [7]≈ 1.33310−4 W
foot-pound-force per hourft lbf/h≡ 1 ft lbf/h≈ 3.766 16110−4 W
atmosphere cubic centimetre per minuteatm ccm≡ 1 atm × 1 cm³/min= 1.688 7510−3 W
foot-pound-force per minuteft lbf/min≡ 1 ft lbf/min= 2.259 696 580 552 33410−2 W
atmosphere–cubic centimetre per secondatm ccs≡ 1 atm × 1 cm³/s= 0.101 325 W
BTU (International Table) per hourBTUIT/h≡ 1 BTUIT/h≈ 0.293 071 W
atmosphere–cubic foot per houratm cfh≡ 1 atm × 1 cu ft/h= 0.797 001 244 704 W
foot-pound-force per secondft lbf/s≡ 1 ft lbf/s= 1.355 817 948 331 400 4 W
litre-atmosphere per minuteL·atm/min≡ 1 atm × 1 L/min= 1.688 75 W
calorie (International Table) per secondcalIT/s≡ 1 calIT/s= 4.1868 W
BTU (International Table) per minuteBTUIT/min≡ 1 BTUIT/min≈ 17.584 264 W
atmosphere-cubic foot per minuteatm·cfm≡ 1 atm × 1 cu ft/min= 47.820 074 682 24 W
square foot equivalent direct radiationsq ft EDR≡ 240 BTUIT/h≈ 70.337 057 W
litre-atmosphere per secondL·atm/s≡ 1 atm × 1 L/s= 101.325 W
horsepower (metric)hp≡ 75 m kgf/s= 735.498 75 W
horsepower (European electrical)hp≡ 75 kp·m/s= 736 W
horsepower (Imperial mechanical)hp≡ 550 ft lbf/s= 745.699 871 582 270 22 W
horsepower (Imperial electrical)hp≡ 746 W
ton of air conditioning ≡ 1 t × 1005 J/kg × 1 °F/K ÷ 10 min= 844.2 W
ponceletp≡ 100 m kgf/s= 980.665 W
BTU (International Table) per secondBTUIT/s≡ 1 BTUIT/s= 1.055 055 852 62103 W
atmosphere-cubic foot per secondatm cfs≡ 1 atm × 1 cu ft/s= 2.869 204 480 934 4103 W
ton of refrigeration (IT) ≡ 1 BTUIT × 1 sh tn/lb ÷ 10 min/s≈ 3.516 853103 W
ton of refrigeration (Imperial) ≡ 1 BTUIT × 1 lng tn/lb ÷ 10 min/s≈ 3.938 875103 W
boiler horsepowerbhp≈ 34.5 lb/h × 970.3 BTUIT/lb≈ 9.810 657103 W

### Angular momentum

Action, Angular momentum, L, J
Name of unit Symbol Definition Relation to SI units
SI unitJ·s≡ kg·m²/s
atomic unit of actionau = /2π≈ 1.054 571 59610−34 J·s
cgs uniterg·s= 10−7 J·s

### Electric current

Electric current, I
Name of unit Symbol Definition Relation to SI units
ampereA(SI base unit)
esu per second; statampere (cgs unit)esu/s≡ (0.1 A·m/s) /c≈ 3.335 64110−10 A
electromagnetic unit; abampere (cgs unit)abamp≡ 10 A

### Electric charge

Electric charge, Q
Name of unit Symbol Definition Relation to SI units
coulomb (SI unit)C≡ A·s
atomic unit of chargeaue≈ 1.602 176 46210−19 C
statcoulomb; franklin; electrostatic unit (cgs unit)statC; Fr; esu≡ (0.1 A·m) /c≈ 3.335 64110−10 C
abcoulomb; electromagnetic unit (cgs unit)abC; emu≡ 10 C
faradayF≡ 1 mol × NA·e≈ 96,485.3383 C

### Electromotive force

Voltage, Electromotive force, U
Name of unit Symbol Definition Relation to SI units
volt (SI unit)V≡ kg·m²/(A·s³)
abvolt (cgs unit)abV≡ 110−8 V
statvolt (cgs unit)statVc· (1 μJ/A·m)= 299.792 458 V

### Electrical resistance

Electrical resistance, R
Name of unit Symbol Definition Relation to SI units
ohm (SI unit)O≡ V/A= kg·m²/(A²·s³)

### Dynamic viscosity

Dynamic viscosity, ?
Name of unit Symbol Definition Relation to SI units
pascal second (SI unit)Pa·s≡ N·s/m²= kg/(m·s)
poise (cgs unit)P≡ 10−1 Pa·s

### Kinematic viscosity

Kinematic viscosity, ?
Name of unit Symbol Definition Relation to SI units
SI unitm²/s≡ m²/s
stokes (cgs unit)St≡ 10−4 m²/s

### Information entropy

Information entropy, H
Name of unit Symbol Definition Relation to SI units
SI unitJ/K≡ 1 J/K
nat; nip; nepitnatkB= 1.3806505(23) × 10−23 J/K
bit; shannonbit; b; Sh≡ ln(2) × kB= 9.569940(16) × 10−24 J/K
ban; hartleyban; Hart≡ ln(10) × kB= 3.1790653(53) × 10−23 J/K
nibble≡ 4 bits= 3.8279760(64) × 10−23 J/K
byteB≡ 8 bits= 7.655952(13) × 10−23 J/K
kilobyte (kibibyte)KB; KiB≡ 1024 B= 7.839695(13) × 10−23 J/K

### Temperature

Temperature, T
Name of unit Symbol Relation to SI units Relation to °C
kelvinKSI base unitT[K] = T[°C] + 273.15
degree Celsius°CT[°C] = T[K] − 273.15
degree Rankine°R; °RaT[°Ra] = 1.8 × T[K]
degree Fahrenheit°FT[°F] = T[K] × 1.8 − 459.67T[°F] = 1.8 × T[°C] + 32

## Software tools

Home and office computers come with converters in bundled spreadsheet applications or can access free converters via the Internet. Units and measurements can be easily converted using these tools, but only if the units are explicitly defined and the conversion is compatible (e.g., cmHg to kPa).

### Free conversion software

:`120 m/s in mph`     or     `200 lb in stone`

### General commercial sources of converters

• Advanced electronic calculators have unit-conversion functionality.
• Spreadsheet programs usually provide conversion functions or formulas or the user can write their own.
• Commercial mathematical, scientific and technical applications often include converters.

## References

1. ^ National Bureau of Standards. (June 30, 1959). Refinement of values for the yard and the pound. Federal Register, viewed September 20, 2006 at National Geodetic Survey web site.
2. ^ P. Kenneth Seidelmann, Ed. (1992). Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books. p. 716 and s.v. parsec in Glossary.
3. ^ The Swiss Federal Office for Metrology gives Zentner on a German language web page[2] and quintal on the English translation of that page[3]; the unit is marked "spécifiquement suisse !"
4. ^ Rowlett, Russ. A Dictionary of Units of Measurement. Viewed October 14, 2006 at [4]
5. ^ Barry N. Taylor, (April 1995), Guide for the Use of the International System of Units (SI) (NIST Special Publication 811), Washington, DC: U.S. Government Printing Office, pp. 64–65.
6. ^ Barry N. Taylor, (April 1995), Guide for the Use of the International System of Units (SI) (NIST Special Publication 811), Washington, DC: U.S. Government Printing Office, p. 5.
7. ^ Russ Rowlett. (2005). How Many: A Dictionary of Units of Measure. Viewed 5 November 2006 at [5]
• Klein, Herbert. 1988. The science of measurement: A historical survey. New York: Dover Publications.

units of measurement have played a crucial role in human endeavour from early ages up to this day. Disparate systems of measurement used to be very common. Now there is a global standard, the International System (SI) of units, the modern form of the metric system.
Quantity is a kind of property which exists as magnitude or multitude. It is among the basic classes of things along with quality, substance, change, and relation. Quantity was first introduced as quantum, an entity having quantity.
Rounding to n significant figures is a form of rounding. Significant figures (also called significant digits) can also refer to a crude form of error representation based around significant figure rounding. For this use, see Significance arithmetic.
Rounding to n significant figures is a form of rounding. Significant figures (also called significant digits) can also refer to a crude form of error representation based around significant figure rounding. For this use, see Significance arithmetic.
Length is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end. This may be distinguished from height, which is vertical extent, and width or breadth
Si, si, or SI may refer to (all SI unless otherwise stated):

In language:
• One of two Italian words:
• (accented) for "yes"
• si

1 ångström =
SI units
010−12 m 010−3 nm
Natural units
01024 lPa0
US customary / Imperial units
010−12 ft 010−9
1 astronomical unit =
SI units
0109 m 0106 km
Astronomical units
010-6 pc 010−6 ly
US customary / Imperial units
0109 ft 0106 mi
The
Atomic units (au) form a system of units convenient for atomic physics, electromagnetism, and quantum electrodynamics, especially when the focus is on the properties of electrons.
SI units
010−12 m 010−3 nm
Natural units
01024 lP 0103 le
US customary / Imperial units
010−12 ft 010
The fine-structure constant or Sommerfeld fine-structure constant, usually denoted , is the fundamental physical constant characterizing the strength of the electromagnetic interaction.

A cable length or cable's length is a nautical unit of measure equal to one tenth of a nautical mile or 100 fathoms. The unit is named after the length of a ship's anchor cable in the age of sail. The definition varies:
• International: 1/10 nautical mile, or 185.

caliber or calibre designates the interior diameter of a tube or the exterior diameter of a wire or rod. It comes from the Italian calibro, itself from qālib (قالب), Arabic word for mold.
1 chain =
SI units
0 m 0 cm
US customary / Imperial units
0 ft 0 yd

A chain is a unit of length; it measures 66 feet, which equates to 20.1168 metres). There are therefore 80 chains in one statute mile.
Edmund Gunter (1581 - December 10, 1626), English mathematician, of Welsh extraction, was born in Hertfordshire in 1581.

He was educated at Westminster School, and in 1599 was elected a student of Christ Church, Oxford.
1 chain =
SI units
0 m 0 cm
US customary / Imperial units
0 ft 0 yd

A chain is a unit of length; it measures 66 feet, which equates to 20.1168 metres). There are therefore 80 chains in one statute mile.
Jesse Ramsden (October 6, 1735 - November 5, 1800) was an English astronomical and scientific instrument maker.

Ramsden was born at Salterhebble near Halifax, West Yorkshire, England.
1 fathom =
SI units
0 m 0 cm
US customary / Imperial units
0 ft 0 in
A fathom is a unit of length in the Imperial system (and the derived U.S. customary units).
1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
1 foot =
SI units
0 m 0 mm
US customary / Imperial units
0 yd 0 in
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes,
1 foot =
SI units
0 m 0 mm
US customary / Imperial units
0 yd 0 in
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes,
1 foot =
SI units
0 m 0 mm
US customary / Imperial units
0 yd 0 in
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes,
1 foot =
SI units
0 m 0 mm
US customary / Imperial units
0 yd 0 in
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes,
1 foot =
SI units
0 m 0 mm
US customary / Imperial units
0 yd 0 in
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes,
1 foot =
SI units
0 m 0 mm
US customary / Imperial units
0 yd 0 in
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes,
1 furlong =
SI units
0 m 0 km
US customary / Imperial units
0 ft 0 yd
A furlong is a measure of distance within imperial units and U.S. customary units, and is equal to 660 feet or one-eighth of a mile. In metric units, this is 201.
1 geographical mile =
SI units
0 m 0 km
US customary / Imperial units
0 ft 0 mi
The geographical mile is a unit of length determined by 1 minute of arc along the Earth's equator, approximately equal to 1855.325 metres (6087.
1 inch =
SI units
010−3 m 0 mm
US customary / Imperial units
010−3 ft 010−3 yd

An inch (plural: inches; symbol or abbreviation: in or, sometimes,