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

Legend

=	definition
=	exactly equal to
?	approximately equal to
(digits)	indicates the digits repeat infinitely

Length

Length, l

Name of unit	Symbol	Definition	Relation to SI units
ångström	Å		≡ 110−10 m = 0.1 nm
astronomical unit	AU	Mean distance from Earth to the Sun	= 149 597 870.691 ± 0.030 km
atomic unit of length	au	≡ a0	≈ 5.291 772 08310−11 ± 1910−20 m
barley corn		≡ 1/3 in	≈ 8.466 667 mm
Bohr radius	a0; b	≡ α/(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
calibre	cal	≡ 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
ell	ell	≡ 45 in	= 1.143 m
fathom	fm	≡ 6 ft	= 1.8288 m
		≈ 1/1000 NM	= 1.852 m
fermi	fm	≡ 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
furlong	fur	≡ 660 ft (10 chains)	= 201.168 m
geographical mile	mi	≡ 6082 ft	= 1853.7936 m
hand		≡ 4 in	= 0.1016 m
inch	in	≡ 1/36 yd	= 25.4 mm
league	lea	≡ 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-year	l.y.	≡ c0 × 86 400 × 365.25	= 9.460 730 472 580 81015 m
line	ln	≡ 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
micron	µ		≡ 1.00010−6 m
mil; thou	mil	≡ 1.00010−3 in	= 2.5410−5 m
mil (Sweden and Norway)	mil	≡ 10 km	= 10000 m
mile	mi	≡ 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 league	NL; nl	≡ 3 NM	= 5556 m
nautical mile	NM; nmi	≡ 1852 m	≡ 1852 m
nautical mile (Admiralty)	NM (Adm); nmi (Adm)	≡ 6080 ft	= 1853.184 m
pace		≡ 2.5 ft	= 0.762 m
palm		≡ 3 in	= 76.2 mm
parsec	pc	≈ 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; perch	rd	≡ 16 ½ ft	= 5.0292 m
rope	rope	≡ 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 mile	mi	≡ 6087 ft	= 1855.3176 m
twip	twp	≡ 1/1440 in	≈ 1.763 88910−5 m
x unit; siegbahn	xu		≈ 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
acre	ac	≡ 10 sq ch = 4840 sq yd	= 4046.856 422 4 m²
are	a		≡ 100 m²
barn	b		≡ 10−28 m²
barony		≡ 4000 ac	= 1.618 742 568 96107 m²
board	bd	≡ 1 in × 1 ft	= 7.741 9210−3 m²
boiler horsepower equivalent direct radiation	bhp EDR	≡ (1 ft²) (1 bhp) / (240 BTUIT/h)	≈ 12.958 174 m²
circular inch	circ in	≡ π/4 in²	≈ 5.067 07510−4 m²
circular mil; circular thou	circ mil	≡ π/4 mil²	≈ 5.067 07510−10 m²
cord		≡ 192 bd	= 1.486 448 64 m²
dunam		≡ 1000 m²	= 1000 m²
hectare	ha	≡ 10 000 m²	= 0.01 km²
hide		≡ 100 ac	= 4.046 856 422 4105 m²
rood	ro	≡ ¼ ac	= 1011.714 105 6 m²
square chain	sq ch	≡ 1 ch²	= 404.685 642 24 m²
square foot	sq ft	≡ 1 ft²	= 9.290 30410−2 m²
square inch	sq in	≡ 1 in²	= 6.451610−4 m²
square kilometre	km²	≡ 1 km²	= 106 m²
square link	sq lnk	≡ 1 lnk²	= 4.046 856 422 410−2 m²
square metre (SI unit)	m²	≡ 1 m × 1 m	= 1 m²
square mil; square thou	sq mil	≡ 1 mil²	= 6.451610−10 m²
square mile; section	sq mi	≡ 1 mi²	= 2.589 988 110 336106 m²
square rod/pole/perch	sq rd	≡ 1 rd²	= 25.292 852 64 m²
square U.S. Survey foot	sq ft	≡ 1 ft (US)²	≈ 9.290 341 161 327 4910-2 m²
square U.S. Survey mile	sq mi	≡ 1 mi (US)²	≈ 2.589 998106 m²
square yard	sq yd	≡ 1 yd²	= 0.836 127 36 m²
stremma		≡ 1000 m²	= 1000 m²
township		≡ 36 sq mi (US)	≈ 9.323 994107 m²
yardland		≡ 30 ac	= 1.214 056 926 72105 m²

Volume

Volume, V

Name of unit	Symbol	Definition	Relation to SI units
cubic metre (SI unit)	m³	≡ 1 m × 1 m × 1 m
litre	L		≡ 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. fluidram	fl 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 inch	cu 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); Noggin	gi (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-foot	fbm	≡ 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 gallon	beer 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 foot	cu 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
perch	per	≡ 16½ ft × 1½ ft × 1 ft	= 0.700 841 953 152 m³
cubic yard	cu 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 fathom	cu 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 mile	cu mi	≡ 1 mi³	= 4.168 181 825 440 579 584 km³

Angle

Angle

Name of unit	Symbol	Definition	Relation to SI units
radian (SI unit)	rad		≡ 1 rad
centesimal second of arc	"	≡ 1 gr/10000	≈ 1.570 796 µrad
arcsecond	"	≡ 1°/3600	≈ 4.848 137 µrad
centesimal minute of arc	'	≡ 1 gr/100	≈ 0.157 080 mrad
minute of arc	'	≡ 1°/60	≈ 0.290 888 mrad
angular mil	µ	≡ 2π/6400 rad	≈ 0.981 748 mrad
grad; gradian; gon	gr	≡ 2π/400 rad = 0.9°	≈ 15.707 963 mrad
degree (of arc)	°	≡ π/180 rad	≈ 17.453 293 mrad
sign		≡ 30°	≈ 0.523 599 rad
octant		≡ 45°	≈ 0.785 398 rad
sextant		≡ 60°	≈ 1.047 198 rad
quadrant		≡ 90°	≈ 1.570 796 rad

Solid angle

Solid angle

Name of unit	Symbol	Definition	Relation to SI units
steradian	sr		(SI derived unit)

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, grave	kg; G		(SI base unit)
electron rest mass	me		≈ 9.109 381 8810−31 ± 7210−39 kg
atomic unit of mass	au	≡ me	≈ 9.109 381 8810−31 ± 7210−39 kg
unified atomic mass unit	u		≈ 1.660 538 7310−27 ± 1310−35 kg
dalton	Da		≈ 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
grain	gr		≡ 64.798 91 mg
crith			≈ 89.9349 mg
carat (metric)	kt		≡ 200 mg
carat	kt	≡ 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
pennyweight	dwt; 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
stone	st	≡ 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; geepound	slug	≡ 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; cental	sh cwt	≡ 100 lb av	= 45.359 237 kg
long hundredweight	long 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
kip	kip	≡ 1000 lb av	= 453.592 37 kg
short ton	sh tn	≡ 2000 lb	= 907.184 74 kg
tonne (mts unit)	t		≡ 1000 kg
long ton	long tn or ton	≡ 2240 lb	= 1016.046 908 8 kg
barge		≡ 22 ½ sh tn	= 20,411.656 65 kg
Zentner	Ztr.		Definitions vary; see [3] and [4]. See also discussion at

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
second	s		(SI base unit)
Planck time		≡ √(Gℏ/c5)	≈ 1.351 211 81810−43 s
atomic unit of time	au	≡ a0/(α·c)	≈ 2.418 884 25410−17 s
svedberg	S	≡ 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
minute	min		≡ 60 s
milliday	md	≡ 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
hour	h	≡ 60 min	= 3600 s
day	d	≡ 24 h	= 86 400 s
week	wk	≡ 7 d	= 604 800 s
fortnight		≡ 2 wk	= 1 209 600 s
month (hollow)	mo	≡ 29 d	= 2 505 600 s
month	mo	≡ 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 year	a 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 hour	fph	≡ 1 ft/h	≈ 8.466 66710−5 m/s
furlong per fortnight		≡ ½ fur/wk	≈ 1.663 09510−4 m/s
inch per minute	ipm	≡ 1 in/min	≈ 4.23 33310−4 m/s
foot per minute	fpm	≡ 1 ft/min	= 5.0810−3 m/s
inch per second	ips	≡ 1 in/s	= 2.5410−2 m/s
kilometre per hour	km/h	≡ 1 km/h	≈ 2.777 77810−1 m/s
foot per second	fps	≡ 1 ft/s	= 3.04810−1 m/s
mile per hour	mph	≡ 1 mi/h	= 0.447 04 m/s
knot	kn	≡ 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 minute	mpm	≡ 1 mi/min	= 26.8224 m/s
mile per second	mps	≡ 1 mi/s	= 1.609 344 km/s
speed of light in vacuum	c	≡ 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 second	fph/s	≡ 1 ft/(h·s)	≈ 8.466 66710−5 m/s²
inch per minute per second	ipm/s	≡ 1 in/(min·s)	≈ 4.233 33310−4 m/s²
foot per minute per second	fpm/s	≡ 1 ft/(min·s)	= 5.0810−3 m/s²
galileo	Gal	≡ 1 cm/s²	= 10−2 m/s²
inch per second squared	ips²	≡ 1 in/s²	= 2.5410−2 m/s²
foot per second squared	fps²	≡ 1 ft/s²	= 3.04810−1 m/s²
mile per hour per second	mph/s	≡ 1 mi/(h·s)	= 4.470410−1 m/s²
knot per second	kn/s	≡ 1 kn/s	≈ 5.144 44410−1 m/s²
standard gravity	g		≡ 9.806 65 m/s²
mile per minute per second	mpm/s	≡ 1 mi/(min·s)	= 26.8224 m/s²
mile per second squared	mps²	≡ 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 force	au	≡ me·α²·c²/a0	≈ 8.238 722 24110−8 N
dyne (cgs unit)	dyn	≡ g·cm/s²	ljm = 10−5 N
milligrave-force, gravet-force	mGf; gf	≡ g × 1 g	= 9.806 65 mN
poundal	pdl	≡ 1 lb·ft/s²	= 0.138 254 954 376 N
ounce-force	ozf	≡ g × 1 oz	= 0.278 013 850 953 781 2 N
pound-force	lbf	≡ g × 1 lb	= 4.448 221 615 260 5 N
kilogram-force; kilopond; grave-force	kgf; kp; Gf	≡ g × 1 kg	= 9.806 65 N
sthene (mts unit)	sn	≡ 1 t·m/s²	= 1 kN
kip; kip-force	kip; kipf; klbf	≡ g × 1000 lb	= 4.448 221 615 260 5 kN
ton-force	tnf	≡ g × 1 sh tn	= 8.896 443 230 521 kN

See also: Conversion between weight (force) and mass

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]
bar	bar		≡ 105 Pa
barye (cgs unit)		≡ 1 dyn/cm²	= 0.1 Pa
centimetre of mercury	cmHg	≡ 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 millimetre	kgf/mm²	≡ 1 kgf/mm²	= 9.806 65 MPa [5]
kip per square inch	ksi	≡ 1 kipf/sq in	≈ 6.894757 MPa [5]
millimetre of mercury	mmHg	≡ 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 foot	psf	≡ 1 lbf/ft²	≈ 47.880 25 Pa [5]
poundal per square foot	pdl/sq ft	≡ 1 pdl/sq ft	≈ 1.488 164 Pa [5]
pound per square inch	psi	≡ 1 lbf/in²	≈ 6.894 757 kPa [5]
short ton per square foot		≡ 1 sh tn × g / 1 sq ft	≈ 95.760 518 kPa
torr	torr	≡ 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
electronvolt	eV	≡ e × 1 V	≈ 1.602 17610−19 J
rydberg	Ry	≡ R∞·ℎ·c	≈ 2.179 87210−18 J
hartree	Eh	≡ me·α²·c² (= 2 Ry)	≈ 4.359 74410−18 J
atomic unit of energy	au	≡ Eh	≈ 4.359 74410−18 J
erg (cgs unit)	erg	≡ 1 g·cm²/s²	= 10−7 J
foot-poundal	ft pdl	≡ 1 lb·ft²/s²	= 4.214 011 009 380 4810−2 J
cubic centimetre of atmosphere; standard cubic centimetre	cc atm; scc	≡ 1 atm × 1 cm³	= 0.101 325 J
inch-pound force	in lbf	≡ g × 1 lb × 1 in	= 0.112 984 829 027 616 7 J
Foot-pound force	ft lbf	≡ g × 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-atmosphere	l 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 foot	cu ft atm; scf	≡ 1 atm × 1 ft³	= 2.869 204 480 934 4 kJ
kilocalorie; large calorie	kcal; Cal	≡ 1000 calIT	= 4.1868 kJ
cubic yard of atmosphere; standard cubic yard	cu 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-hour	hp·h	≡ 1 hp × 1 h	= 2.6845 MJ
kilowatt-hour; Board of Trade Unit	kW·h; B.O.T.U.	≡ 1 kW × 1 h	= 3.6 MJ
thermie	th	≡ 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 TNT	tTNT	≡ 1 Gcalth	= 4.184 GJ
barrel of oil equivalent	bboe	≈ 5.8 MBTU59 °F	≈ 6.12 GJ
ton of coal equivalent	TCE	≡ 7 Gcalth	= 29.3076 GJ
ton of oil equivalent	TOE	≡ 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
lusec	lusec	≡ 1 L·µmHg/s [7]	≈ 1.33310−4 W
foot-pound-force per hour	ft lbf/h	≡ 1 ft lbf/h	≈ 3.766 16110−4 W
atmosphere cubic centimetre per minute	atm ccm	≡ 1 atm × 1 cm³/min	= 1.688 7510−3 W
foot-pound-force per minute	ft lbf/min	≡ 1 ft lbf/min	= 2.259 696 580 552 33410−2 W
atmosphere–cubic centimetre per second	atm ccs	≡ 1 atm × 1 cm³/s	= 0.101 325 W
BTU (International Table) per hour	BTUIT/h	≡ 1 BTUIT/h	≈ 0.293 071 W
atmosphere–cubic foot per hour	atm cfh	≡ 1 atm × 1 cu ft/h	= 0.797 001 244 704 W
foot-pound-force per second	ft lbf/s	≡ 1 ft lbf/s	= 1.355 817 948 331 400 4 W
litre-atmosphere per minute	L·atm/min	≡ 1 atm × 1 L/min	= 1.688 75 W
calorie (International Table) per second	calIT/s	≡ 1 calIT/s	= 4.1868 W
BTU (International Table) per minute	BTUIT/min	≡ 1 BTUIT/min	≈ 17.584 264 W
atmosphere-cubic foot per minute	atm·cfm	≡ 1 atm × 1 cu ft/min	= 47.820 074 682 24 W
square foot equivalent direct radiation	sq ft EDR	≡ 240 BTUIT/h	≈ 70.337 057 W
litre-atmosphere per second	L·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
poncelet	p	≡ 100 m kgf/s	= 980.665 W
BTU (International Table) per second	BTUIT/s	≡ 1 BTUIT/s	= 1.055 055 852 62103 W
atmosphere-cubic foot per second	atm 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 horsepower	bhp	≈ 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 unit	J·s		≡ kg·m²/s
atomic unit of action	au	≡ ℏ = ℎ/2π	≈ 1.054 571 59610−34 J·s
cgs unit	erg·s		= 10−7 J·s

Electric current

Electric current, I

Name of unit	Symbol	Definition	Relation to SI units
ampere	A		(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 charge	au	≡ e	≈ 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
faraday	F	≡ 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)	statV	≡ c· (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 unit	m²/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 unit	J/K		≡ 1 J/K
nat; nip; nepit	nat	≡ kB	= 1.3806505(23) × 10−23 J/K
bit; shannon	bit; b; Sh	≡ ln(2) × kB	= 9.569940(16) × 10−24 J/K
ban; hartley	ban; Hart	≡ ln(10) × kB	= 3.1790653(53) × 10−23 J/K
nibble		≡ 4 bits	= 3.8279760(64) × 10−23 J/K
byte	B	≡ 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
kelvin	K	SI base unit	T[K] = T[°C] + 273.15
degree Celsius	°C	T[°C] = T[K] − 273.15
degree Rankine	°R; °Ra	T[°Ra] = 1.8 × T[K]
degree Fahrenheit	°F	T[°F] = T[K] × 1.8 − 459.67	T[°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

• Units (Unix program) — a popular command-line utility.
• UDUNITS — a similar utility and programming library
• Convert — free downloadable executable for Windows
• Unit Converter Software — free download for Windows*
• Google — many conversions can be performed by typing the source and target units directly in the Google search box, using the keyword in, as explained in Google Calculator Help. For example:

: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

• Klein, Herbert. 1988. The science of measurement: A historical survey. New York: Dover Publications.

See also

External links

• A dictionary of units of measurement
• NIST: Fundamental physical constants — Non-SI units (PDF)
• British law: Units of measurement regulations 1995
• The Unified Code for Units of Measure
• Units, Symbols, and Conversions XML Dictionary
• Online Conversion Chart