Conversion of units

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

Techniques

Rounding of results

The process of making a conversion cannot produce a more precise result than the original quoted figure. Appropriate rounding of results is normally performed after conversion. (See significant figures).

Tables of conversion factors

This article gives lists of conversion factors for each of a number of physical quantities, which are listed in the index. For each physical quantity, a number of different units (some only of historical interest) are shown and expressed in terms of the corresponding SI unit.

Legend

Legend

≡	definition
=	exactly equal to
≈	approximately equal to
digits	indicates that digits repeat infinitely (i.e. 8.294 369 corresponds to 8.294 369 369 369 369 ...)
(H)	of chiefly historical interest

Luminance

Luminance

Name of unit	Symbol	Definition	Relation to SI units
candela per square metre (SI base unit)		≡ cd/m2	= 1 cd/m2
lambert	L	≡ (104/π) cd/m2	≈ 3183.09886 cd/m2

Length

Length

Name of unit	Symbol	Definition	Relation to SI units
metre (SI base unit)	m	≡ 1 m	= 1 m
ångström	Å	= 0.1 nm	≡ 1×10−10 m
astronomical unit	AU	Mean distance from Earth to the Sun	= 149 597 870 691 ± 30 m
atomic unit of length	a0	≡ Bohr radius of hydrogen	≈ 5.29 177 208 59×10−11 ± 3.6×10−20 m
barley corn (H)		≡ ⅓ in (see note above about rounding)	≈ 0.008 m
Bohr radius	a0; b	≡ α/4πR∞	≈ 5.291 772 083×10−11 ± 19×10−20 m
cable length (Imperial)		≡ 608 ft	= 185.3184 m
cable length (International)		≡ 1/10 nmi	= 185.2 m
cable length (U.S.)		≡ 720 ft	= 219.456 m
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 (H)		≈ 18 in	≈ 0.5 m
ell (H)	ell	≡ 45 in	= 1.143 m
fathom	fm	≡ 6 ft	= 1.8288 m
fathom	fm	≈ 1/1000 nmi	= 1.852 m
fermi	fm	≡ 1×10−15 m	= 1×10−15 m
finger		≡ 7/8 in	= 0.022 225 m
finger (cloth)		≡ 4 ½ in	= 0.1143 m
foot (Benoît)(H)	ft (Ben)		≈ 0.304 799 735 m
foot (Clarke's; Cape)(H)	ft (Cla)		≈ 0.304 797 265 4 m
foot (Indian)(H)	ft Ind		≈ 0.304 799 514 m
foot (International)	ft	≡ 12 inches = 1/3 yd	= 0.3048 m
foot (Sear's)(H)	ft (Sear)		≈ 0.304 799 47 m
foot (U.S. Survey)(H)	ft (US)	≡ 1200/3937 m	≈ 0.304 800 610 m
french; charriere	F	≡ 1/3 mm	= 3.3 ×10−4 m
furlong	fur	≡ 10 chains = 660 ft =220 yd	= 201.168 m
geographical mile (H)		≡ 6082 ft	= 1853.7936 m
hand		≡ 4 in	= 0.1016 m
inch	in	≡ 1/36 yd = 1/12 ft	= 0.0254 m
league	lea	≡ 3 mi	= 4828.032 m
light-day		≡ 24 light-hours	= 2.590 206 837 12×1013 m
light-hour		≡ 60 light-minutes	= 1.079 252 848 8×1012 m
light-minute		≡ 60 light-seconds	= 1.798 754 748×1010 m
light-second			≡ 2.997 924 58×108 m
light-year	l.y.	≡ c0 × 86 400 × 365.25	= 9.460 730 472 580 8×1015 m
line	ln	≡ 1/12 in (Klein 1988, 63)	= 0.002 116 m
link (Gunter's; Surveyor's)	lnk	≡ 1/100 ch	= 0.201 168 m
link (Ramsden's; Engineer's)	lnk	≡ 1 ft	= 0.3048 m
mickey		≡ 1/200 in	= 1.27×10−4 m
micron	µ		≡ 1×10−6 m
mil; thou	mil	≡ 1×10−3 in	= 2.54×10−5 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	= 0.05715 m
nautical league	NL; nl	≡ 3 nmi	= 5556 m
nautical mile(international)	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	= 0.0762 m
parsec	pc		= 3.08567782 ×1016 ± 6×106 m
point (ATA)	pt	≡ 0.013837 in	= 0.000 351 459 8 m
point (Didot; European)	pt		≡ 0.000 376 065 m
point (metric)	pt	≡ 3/8 mm	= 0.000 375 m
point (PostScript)	pt	≡ 1/72 in	= 0.000 352 7 m
quarter		≡ ¼ yd	= 0.2286 m
rod; pole; perch (H)	rd	≡ 16 ½ ft	= 5.0292 m
rope (H)	rope	≡ 20 ft	= 6.096 m
span (H)		≡ 6 in	= 0.1524 m
span (cloth) (H)		≡ 9 in	= 0.2286 m
spat		≡ 1012 m	= 1×1012 m
stick (H)		≡ 2 in	= 0.05 08 m
stigma; pm		≡ 1×10−12 m	≡ 1×10−12 m
telegraph mile (H)	mi	≡ 6087 ft	= 1855.3176 m
twip	twp	≡ 1/1440 in	= 1.763 8×10−5 m
x unit; siegbahn	xu		≈ 1.0021×10−13 m
yard (International)	yd	≡3 ft ≡ 36 in	= 0.9144 m

Area

Area

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 96×107 m²
board	bd	≡ 1 in × 1 ft	= 7.741 92×10−3 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 sq in	≈ 5.067 075×10−4 m²
circular mil; circular thou	circ mil	≡ π/4 mil²	≈ 5.067 075×10−10 m²
cord		≡ 192 bd	= 1.486 448 64 m²
dunam		≡ 1000 m²	= 1000 m²
hectare	ha	≡ 10 000 m²	= 10 000 m²
hide		≡ 100 ac	= 4.046 856 422 4×105 m²
rood	ro	≡ ¼ ac	= 1011.714 105 6 m²
shed			≡ 10−52 m²
square chain	sq ch	≡ 1 sq ch	= 404.685 642 24 m²
square foot	sq ft	≡ 1 ft × 1 ft	= 9.290 304×10−2 m²
square inch	sq in	≡ 1 in × 1 in	= 6.4516×10−4 m²
square kilometre	km²	≡ 1 km²	= 106 m²
square link	sq lnk	≡ 1 lnk²	= 4.046 856 422 4×10−2 m²
square metre (SI unit)	m²	≡ 1 m × 1 m	= 1 m²
square mil; square thou	sq mil	≡ 1 mil × 1 mil	= 6.4516×10−10 m²
square mile; section	sq mi	≡ 1 mi × 1 mi	= 2.589 988 110 336×106 m²
square rod/pole/perch	sq rd	≡ 1 sq rd	= 25.292 852 64 m²
square U.S. Survey foot	sq ft	≡ 1 sq ft (US)	≈ 9.290 341 161 327 49×10−2 m²
square U.S. Survey mile	sq mi	≡ 1 sq mi (US)	≈ 2.589 998×106 m²
square yard	sq yd	≡ 1 yd × 1 yd	= 0.836 127 36 m²
stremma		≡ 1000 m²	= 1000 m²
township		≡ 36 sq mi (US)	≈ 9.323 994×107 m²
yardland		≡ 30 ac	= 1.214 056 926 72×105 m²

Volume

Volume

Name of unit	Symbol	Definition	Relation to SI units
acre foot	ac ft	≡ 1 ac x 1 ft = 43560 ft³	= 1 233.481 837 547 52 m³
cubic metre (SI unit)	m³	≡ 1 m × 1 m × 1 m	= 1 m³
litre	L	≡ 1 dm³	= 0.001 m³
lambda	λ	≡ 1 mm³	= 1 ×10−9 m³
drop (metric)		≡ 1/20 mL	= 50.0 ×10−9 m³
minim (Imperial)	min	≡ 1/480 fl oz (Imp) = 1/60 fl dr (Imp)	= 59.193 880 2083 ×10−9 m³
minim (U.S.)	min	≡ 1/480 US fl oz = 1/60 US fl dr	= 61.611 519 921 875 ×10−9 m³
drop (U.S.) (alt)	gtt	≡ 1/456 US fl oz	≈ 64.854 231 ×10−9 m³
drop (Imperial) (alt)	gtt	≡ 1/1824 gi (Imp)	≈ 77.886 684 ×10−9 m³
drop (U.S.)	gtt	≡ 1/360 US fl oz	= 82.148 693 229 16 ×10−9 m³
drop (medical)		≡ 1/12 ml	= 83.03 ×10−9 m³
drop (Imperial)	gtt	≡ 1/288 fl oz (Imp)	= 98.656 467 0138 ×10−9 m³
dash (U.S.)		≡ 1/96 US fl oz = ½ US pinch	= 308.057 599 609 375 ×10−9 m³
dash (Imperial)		≡ 1/384 gi (Imp) = ½ pinch (Imp)	= 369.961 751 302 08 3 ×10−9 m³
pinch (U.S.)		≡ 1/48 US fl oz = ⅛ US tsp	= 616.115 199 218 75 ×10−9 m³
pinch (Imperial)		≡ 1/192 gi (Imp) = ⅛ tsp (Imp)	= 739.923 502 604 16 ×10−9 m³
fluid scruple (Imperial)	fl s	≡ 1/24 fl oz (Imp)	= 1.183 877 604 16 ×10−6 m³
fluid drachm (Imperial)	fl dr	≡ ⅛ fl oz (Imp)	= 3.551 632 812 5 ×10−6 m³
fluid dram (U.S.); U.S. fluidram	fl dr	≡ ⅛ US fl oz	= 3.696 691 195 312 5 ×10−6 m³
teaspoon (Canadian)	tsp	≡ 1/6 fl oz (Imp)	= 4.735 510 41 6 ×10−6 m³
teaspoon (U.S.)	tsp	≡ 1/6 US fl oz	= 4.928 921 595 ×10−6 m³
teaspoon (metric)			≡ 5.0 ×10−6 m³
teaspoon (Imperial)	tsp	≡ 1/24 gi (Imp)	= 5.919 388 020 83 ×10−6 m³
dessertspoon (Imperial)		≡ 1/12 gi (Imp)	= 11.838 776 0416 ×10−6 m³
tablespoon (Canadian)	tbsp	≡ ½ fl oz (Imp)	= 14.206 531 25 ×10−6 m³
tablespoon (U.S.)	tbsp	≡ ½ US fl oz	= 14.786 764 782 5 ×10−6 m³
tablespoon (metric)			≡ 15.0 ×10−6 m³
cubic inch	cu in	≡ 1 in × 1 in × 1 in	= 16.387 064 ×10−6 m³
tablespoon (Imperial)	tbsp	≡ 5/8 fl oz (Imp)	= 17.758 164 062 5 ×10−6 m³
pony		≡ 3/4 US fl oz	= 22.180 147 171 875 ×10−6 m³
fluid ounce (Imperial)	fl oz (Imp)	≡ 1/160 gal (Imp)	= 28.413 062 5 ×10−6 m³
fluid ounce (U.S.)	US fl oz	≡ 1/128 gal (US)	= 29.573 529 562 5 ×10−6 m³
shot		≡ 1 US fl oz	≈ 29.57 ×10−6 m³
jigger		≡ 1½ US fl oz	≈ 44.36 ×10−6 m³
gill (U.S.)	gi (US)	≡ 4 US fl oz	= 118.294 118 25 ×10−6 m³
gill (Imperial); Noggin	gi (Imp); nog	≡ 5 fl oz (Imp)	= 142.065 312 5 ×10−6 m³
cup (Canadian)	c (CA)	≡ 8 fl oz (Imp)	= 227.304 5 ×10−6 m³
cup (U.S.)	c (US)	≡ 8 US fl oz ≡ 1/16 gal (US)	= 236.588 236 5 ×10−6 m³
cup (metric)	c		≡ 250.0 ×10−6 m³
breakfast cup		≡ 10 fl oz (Imp)	= 284.130 625 ×10−6 m³
pint (U.S. fluid)	pt (US fl)	≡ ⅛ gal (US)	= 473.176 473 ×10−6 m³
pint (U.S. dry)	pt (US dry)	≡ 1/64 bu (US lvl) ≡ ⅛ gal (US dry)	= 550.610 471 357 5 ×10−6 m³
pint (Imperial)	pt (Imp)	≡ ⅛ gal (Imp)	= 568.261 25 ×10−6 m³
fifth		≡ 1/5 US gal	= 757.082 356 8 ×10−6 m³
quart (U.S. fluid)	qt (US)	≡ ¼ gal (US fl)	= 946.352 946 ×10−6 m³
quart (U.S. dry)	qt (US)	≡ 1/32 bu (US lvl) = ¼ gal (US dry)	= 1.101 220 942 715 ×10−3 m³
quart (Imperial)	qt (Imp)	≡ ¼ gal (Imp)	= 1.136 522 5 ×10−3 m³
pottle; quartern		≡ ½ gal (Imp) = 80 fl oz (Imp)	= 2.273 045 ×10−3 m³
board-foot	fbm	≡ 144 cu in	= 2.359 737 216 ×10−3 m³
gallon (U.S. fluid; Wine)	gal (US)	≡ 231 cu in	= 3.785 411 784 ×10−3 m³
gallon (U.S. dry)	gal (US)	≡ ⅛ bu (US lvl)	= 4.404 883 770 86 ×10−3 m³
gallon (Imperial)	gal (Imp)	≡	= 4.546 09 ×10−3 m³
beer gallon	beer gal	≡ 282 cu in	= 4.621 152 048 ×10−3 m³
peck (U.S. dry)	pk	≡ ¼ US lvl bu	= 8.809 767 541 72 ×10−3 m³
peck (Imperial)	pk	≡ 2 gal (Imp)	= 9.092 18 ×10−3 m³
bucket (Imperial)	bkt	≡ 4 gal (Imp)	= 0.018 184 36 m³
timber foot		≡ 1 cu ft	= 0.028 316 846 592 m³
cubic foot	cu ft	≡ 1 ft × 1 ft × 1 ft	= 0.028 316 846 592 m³
firkin		≡ 9 gal (US)	= 0.034 068 706 056 m³
bushel (U.S. dry level)	bu (US lvl)	≡ 2150.42 cu in	= 0.035 239 070 166 88 m³
bushel (Imperial)	bu (Imp)	≡ 8 gal (Imp)	= 0.036 368 72 m³
bushel (U.S. dry heaped)	bu (US)	≡ 1 ¼ bu (US lvl)	= 0.044 048 837 708 6 m³
strike (U.S.)		≡ 2 bu (US lvl)	= 0.070 478 140 333 76 m³
strike (Imperial)		≡ 2 bu (Imp)	= 0.072 737 44 m³
kilderkin		≡ 18 gal (Imp)	= 0.081 829 62 m³
sack (U.S.)		≡ 3 bu (US lvl)	= 0.105 717 210 500 64 m³
sack (Imperial); bag		≡ 3 bu (Imp)	= 0.109 106 16 m³
barrel (U.S. dry)	bl (US)	≡ 105 qt (US) = 105/32 bu (US lvl)	= 0.115 628 198 985 075 m³
barrel (U.S. fluid)	fl bl (US)	≡ 31½ gal (US)	= 0.119 240 471 196 m³
coomb		≡ 4 bu (Imp)	= 0.145 474 88 m³
barrel (petroleum)	bl; bbl	≡ 42 gal (US)	= 0.158 987 294 928 m³
barrel (Imperial)	bl (Imp)	≡ 36 gal (Imp)	= 0.163 659 24 m³
hogshead (U.S.)	hhd (US)	≡ 2 fl bl (US)	= 0.238 480 942 392 m³
seam		≡ 8 bu (US lvl)	= 0.281 912 561 335 04 m³
quarter; pail		≡ 8 bu (Imp)	= 0.290 949 76 m³
hogshead (Imperial)	hhd (Imp)	≡ 2 bl (Imp)	= 0.327 318 48 m³
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
cubic mile	cu mi	≡ 1 mi × 1 mi × 1 mi	= 4 168 181 825.440 579 584 m³

Angle

Angle

Name of unit	Symbol	Definition	Relation to SI units
radian (SI unit)	rad	≡ 180°/π	1 rad
centesimal second of arc	"	≡ 1 grad/10000	≈ 1.57 079 6×10−6 rad
arcsecond	"	≡ 1°/3600	≈ 4.84 813 7×10−6 rad
centesimal minute of arc	'	≡ 1 grad/100	≈ 15.708 0×10−6 rad
minute of arc	'	≡ 1°/60	≈ 29.088 8×10−6 rad
angular mil	µ	≡ 2π/6400 rad	≈ 9.8174 8×10−4 rad
grad; gradian; gon	grad	≡ 2π/400 rad = 0.9°	≈ 1.570 796 3×10−3 rad
degree (of arc)	°	≡ π/180 rad	≈ 1.745 329 3×10−3 rad
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

Name of unit	Symbol	Definition	Relation to SI units
kilogram (SI base unit)	kg	≡ 1kg – see also grave (mass) (G)	= 1kg
gram	g	1/1000 of the SI base unit kg	= 1×10−3 kg
electron rest mass	me		≈ 9.109 381 88×10−31 ± 72×10−39 kg
atomic unit of mass	au	≡ me	≈ 9.109 381 88×10−31 ± 72×10−39 kg
unified atomic mass unit	u		≈ 1.660 538 73×10−27 ± 13×10−35 kg
dalton	Da		≈ 1.660 902 10×10−27 ± 13×10−35 kg
gamma	γ		≡ 1 ×10−6 kg
MeV/c2	MeV/c2	Also keV/c2, etc. See Electronvolt#As_a_measurement_of_mass.	≈ 1.7827×10−30 kg
point		≡ 1/100 kt (metric)	= 2 ×10−6 kg
mite		≡ 1/20 gr	= 3.239 945 5 ×10−6 kg
mite (metric)		≡ 1/20 g	= 50 ×10−6 kg
grain	gr		≡ 64.798 91 ×10−6 kg
crith			≈ 89.9349 ×10−6 kg
carat (metric)	ct		≡ 200 ×10−6 kg
carat	kt	≡ 3 1/6 gr	≈ 205.196 548 333 ×10−6 kg
sheet		≡ 1/700 lb av	= 647.9891 ×10−6 kg
scruple (apothecary)	s ap	≡ 20 gr	= 1.295 978 2 ×10−3 kg
pennyweight	dwt; pwt	≡ 1/20 oz t	= 1.555 173 84 ×10−3 kg
dram (avoirdupois)	dr av	≡ 27 11/32 gr	= 1.771 845 195 312 5 ×10−3 kg
dram (apothecary; troy)	dr t	≡ 60 gr	= 3.887 934 6 ×10−3 kg
hyl (CGS unit)		≡ 1 gee × 1 g × 1 s²/m	= 9.806 65 ×10−3 kg
ounce (avoirdupois)	oz av	≡ 1/16 lb	= 28.349 523 125 ×10−3 kg
assay ton (short)	AT	≡ 1 mg × 1 sh tn ÷ 1 oz t	≈ 29.166 667 ×10−3 kg
ounce (apothecary; troy)	oz t	≡ 1/12 lb t	= 31.103 476 8 ×10−3 kg
assay ton (long)	AT	≡ 1 mg × 1 long tn ÷ 1 oz t	≈ 32.666 667 ×10−3 kg
mark		≡ 8 oz t	= 248.827 814 4 ×10−3 kg
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)			≡ 0.5 kg
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 (variants exist)	= 114.305 277 24 kg
long quarter (informal)		≡ ¼ long tn	= 254.011 727 2 kg
quarter (informal)		≡ ¼ short tn	= 226.796 185 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 and . See also discussion at Talk:Conversion of units#Zentner

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 (SI base unit)	s		= 1 s
Planck time		≡ (Gℏ/c5)½	≈ 1.351 211 818×10−43 s
atomic unit of time	au	≡ a0/(α·c)	≈ 2.418 884 254×10−17 s
svedberg	S	≡ 10−13 s	= 100×10−13 s
shake		≡ 10−8 s	= 10×10−8 s
sigma		≡ 10−6 s	= 10×10−6 s
jiffy		≡ 1/60 s	≈ .016667 s
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, y, or yr	≡ 365 d	= 31 536 000 s
year (Gregorian)	a, y, or yr	≡ 365.2425 d	= 31 556 952 s
year (Julian)	a, y, or yr	≡ 365.25 d	= 31 557 600 s
sidereal year	a, y, or yr	≡ 365.256363 d	= 31 558 149.76 s
Olympiad		≡ 4 a of 365 d	= 1.2614×108 s
lustre; lustrum		≡ 5 a of 365 d	= 1.5768×108 s
octaeteris		≡ 8 a of 365 d	= 2.522 88×108 s
decade		≡ 10 a of 365 d	= 3.1536×108 s
enneadecaeteris; Metonic cycle		≡ 110 mo (hollow) + 125 mo (full) = 19 a of 365 d	= 5.996 16×108 s
Callippic cycle		≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d	= 2.398 377 6×109 s
century (Calendar)		≡ 100 a of 365 d	= 3.1536×109 s
century (Julian)		≡ 100 a of 365.25 d	= 3.155 76×109 s
Hipparchic cycle		≡ 4 Callippic cycles - 1 d	= 9.593 424×109 s
millennium (Calendar)		≡ 1000 a of 365 d	= 3.1536×1010 s
millennium (Gregorian)		≡ 1000 a of 365.2425 d	= 3.155 695 2×1010 s
millennium (Julian)		≡ 1000 a of 365.25 d	= 3.155 76×1010 s
Sothic cycle		≡ 1461 a of 365 d	= 4.607 409 6×1010 s

Speed or velocity

Speed

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	≈ 8.466 667×10−5 m/s
furlong per fortnight		≡ furlong/fortnight	≈ 1.663 095×10−4 m/s
inch per minute	ipm	≡ 1 in/min	≈ 4.23 333×10−4 m/s
foot per minute	fpm	≡ 1 ft/min	= 5.08×10−3 m/s
inch per second	ips	≡ 1 in/s	= 2.54×10−2 m/s
kilometre per hour	km/h	≡ 1 km/h	≈ 2.777 778×10−2 m/s
foot per second	fps	≡ 1 ft/s	= 3.048×10−1 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	= 1609.344 m/s
speed of light in vacuum	c	≡ 2.997 924 58×108 m/s	= 2.997 924 58×108 m/s
speed of sound in air	s	≡ 770 mph = 1230 km/h	≈ 344 m/s
mach	M	≡ 331 m/s	≈ 331 m/s

A velocity consists of a speed combined with a direction; the speed part of the velocity takes units of speed.

Acceleration

Acceleration

Name of unit	Symbol	Definition	Relation to SI units
metre per second squared (SI unit)	m/s²	≡ 1 m/s²	= 1 m/s²
foot per hour per second	fph/s	≡ 1 ft/(h·s)	≈ 8.466 667×10−5 m/s²
inch per minute per second	ipm/s	≡ 1 in/(min·s)	≈ 4.233 333×10−4 m/s²
foot per minute per second	fpm/s	≡ 1 ft/(min·s)	= 5.08×10−3 m/s²
galileo	Gal	≡ 1 cm/s²	= 10−2 m/s²
inch per second squared	ips²	≡ 1 in/s²	= 2.54×10−2 m/s²
foot per second squared	fps²	≡ 1 ft/s²	= 3.048×10−1 m/s²
mile per hour per second	mph/s	≡ 1 mi/(h·s)	= 4.4704×10−1 m/s²
knot per second	kn/s	≡ 1 kn/s	≈ 5.144 444×10−1 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	= 1.609 344×103 m/s²

Force

Force

Name of unit	Symbol	Definition	Relation to SI units
newton (SI unit)	N	≡ kg·m/s²	= 1 N
atomic unit of force	au	≡ me·α²·c²/a0	≈ 8.238 722 241×10−8 N
dyne (cgs unit)	dyn	≡ g·cm/s²	= 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 ×10−3 N
kip; kip-force	kip; kipf; klbf	≡ g × 1000 lb	= 4.448 221 615 260 5 ×103 N
ton-force	tnf	≡ g × 1 sh tn	= 8.896 443 230 521 ×103 N

See also: Conversion between weight (force) and mass

Pressure or mechanical stress

Pressure

Name of unit	Symbol	Definition	Relation to SI units
atmosphere (standard)	atm		≡ 101 325 Pa
atmosphere (technical)	at	≡ 1 kgf/cm²	= 9.80665 ×104 Pa
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 ×10−3 Pa
centimetre of water (4 °C)	cmH2O	≈ 999.972 kg/m³ × 1 cm × g	≈ 98.0638 Pa
foot of mercury (conventional)	ftHg	≡ 13 595.1 kg/m³ × 1 ft × g	≈ 40.636 66 ×103 Pa
foot of water (39.2 °F)	ftH2O	≈ 999.972 kg/m³ × 1 ft × g	≈ 2.988 98 ×103 Pa
inch of mercury (conventional)	inHg	≡ 13 595.1 kg/m³ × 1 in × g	≈ 3.386 389 ×103 Pa
inch of water (39.2 °F)	inH2O	≈ 999.972 kg/m³ × 1 in × g	≈ 249.082 Pa
kilogram-force per square millimetre	kgf/mm²	≡ 1 kgf/mm²	= 9.806 65 ×106 Pa
kip per square inch	ksi	≡ 1 kipf/sq in	≈ 6.894757 ×106 Pa
millimetre of mercury	mmHg	≡ 13 595.1 kg/m³ × 1 mm × g ≈ 1 torr	≈ 133.322 4 Pa
millimetre of water (3.98 °C)	mmH2O	≈ 999.972 kg/m³ × 1 mm × g = 0.999972 kgf/m²	= 9.806 38 Pa
pascal (SI unit)	Pa	≡ N/m² = kg/(m·s²)	= 1 Pa
pièze (mts unit)	pz	≡ 1000 kg/m·s²	= 1 ×10−3 Pa
pound per square foot	psf	≡ 1 lbf/ft²	≈ 47.880 25 Pa
poundal per square foot	pdl/sq ft	≡ 1 pdl/sq ft	≈ 1.488 164 Pa
pound per square inch	psi	≡ 1 lbf/in²	≈ 6.894 757 ×10+3 Pa
short ton per square foot		≡ 1 sh tn × g / 1 sq ft	≈ 95.760 518 ×10+3 Pa
torr	torr	≡ 101 325/760 Pa	≈ 133.322 4 Pa

Torque

Torque

Name of unit	Symbol	Definition	Relation to SI units
Newton metre (SI unit)	N·m	≡ N × m = kg·m²/s²	= 1 N·m
foot-poundal	ft pdl	≡ 1 lb·ft²/s²	= 4.214 011 009 380 48×10−2 N·m
inch-pound force	in lbf	≡ g × 1 lb × 1 in	= 0.112 984 829 027 616 7 N·m
foot-pound force	ft lbf	≡ g × 1 lb × 1 ft	= 1.355 817 948 331 400 4 N·m

Energy

Energy

Name of unit	Symbol	Definition	Relation to SI units
joule (SI unit)	J	≡ m·N = W·s = V·A·s = kg·m²/s²	= 1 J
electronvolt	eV	≡ e × 1 V	≈ 1.602 176×10−19 J
rydberg	Ry	≡ R∞·ℎ·c	≈ 2.179 872×10−18 J
hartree	Eh	≡ me·α²·c² (= 2 Ry)	≈ 4.359 744×10−18 J
atomic unit of energy	au	≡ Eh	≈ 4.359 744×10−18 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 48×10−2 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
kilocalorie; large calorie	kcal; Cal	≡ 1000 calIT	= 4.1868 ×103 J
litre-atmosphere	l atm; sl	≡ 1 atm × 1 L	= 101.325 J
gallon-atmosphere (US)	US gal atm	≡ 1 atm × 1 gal (US)	= 383.556 849 013 8 J
gallon-atmosphere (imperial)	imp gal atm	≡ 1 atm × 1 gal (imp)	= 460.632 569 25 J
British thermal unit (thermochemical)	BTUth		≈ 1.054 350 ×103 J
British thermal unit (ISO)	BTUISO		≡ 1.0545 ×103 J
British thermal unit (63 °F)	BTU63 °F		≈ 1.0546 ×103 J
British thermal unit (60 °F)	BTU60 °F		≈ 1.054 68 ×103 J
British thermal unit (59 °F)	BTU59 °F		≡ 1.054 804 ×103 J
British thermal unit (International Table)	BTUIT		= 1.055 055 852 62 ×103 J
British thermal unit (mean)	BTUmean		≈ 1.055 87 ×103 J
British thermal unit (39 °F)	BTU39 °F		≈ 1.059 67 ×103 J
Celsius heat unit (International Table)	CHUIT	≡ 1 BTUIT × 1 K/°R	= 1.899 100 534 716 ×103 J
cubic foot of atmosphere; standard cubic foot	cu ft atm; scf	≡ 1 atm × 1 ft³	= 2.869 204 480 934 4 ×103 J
cubic yard of atmosphere; standard cubic yard	cu yd atm; scy	≡ 1 atm × 1 yd³	= 77.468 520 985 228 8 ×103 J
cubic foot of natural gas		≡ 1000 BTUIT	= 1.055 055 852 62 ×106 J
horsepower-hour	hp·h	≡ 1 hp × 1 h	= 2.684519537696172792 ×106 J
kilowatt-hour; Board of Trade Unit	kW·h; B.O.T.U.	≡ 1 kW × 1 h	= 3.6 ×106 J
thermie	th	≡ 1 McalIT	= 4.1868 ×106 J
therm (U.S.)		≡ 100 000 BTU59 °F	= 105.4804 ×106 J
therm (E.C.)		≡ 100 000 BTUIT	= 105.505 585 262 ×106 J
ton of TNT	tTNT	≡ 1 Gcalth	= 4.184 ×109 J
barrel of oil equivalent	bboe	≈ 5.8 ×106 BTU59 °F	≈ 6.12 ×109 J
ton of coal equivalent	TCE	≡ 7 Gcalth	= 29.3076 ×109 J
ton of oil equivalent	TOE	≡ 10 Gcalth	= 41.868 ×109 J
quad		≡ 1015 BTUIT	= 1.055 055 852 62×1018 J

Power

Power

Name of unit	Symbol	Definition	Relation to SI units
watt (SI unit)	W	≡ J/s = N·m/s = kg·m²/s³	= 1 W
lusec	lusec	≡ 1 L·µmHg/s	≈ 1.333×10−4 W
foot-pound-force per hour	ft lbf/h	≡ 1 ft lbf/h	≈ 3.766 161×10−4 W
atmosphere cubic centimetre per minute	atm ccm	≡ 1 atm × 1 cm³/min	= 1.688 75×10−3 W
foot-pound-force per minute	ft lbf/min	≡ 1 ft lbf/min	= 2.259 696 580 552 334×10−2 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 °R/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 62×103 W
atmosphere-cubic foot per second	atm cfs	≡ 1 atm × 1 cu ft/s	= 2.869 204 480 934 4×103 W
ton of refrigeration (IT)		≡ 1 BTUIT × 1 sh tn/lb ÷ 10 min/s	≈ 3.516 853×103 W
ton of refrigeration (Imperial)		≡ 1 BTUIT × 1 lng tn/lb ÷ 10 min/s	≈ 3.938 875×103 W
boiler horsepower	bhp	≈ 34.5 lb/h × 970.3 BTUIT/lb	≈ 9.810 657×103 W

Angular momentum

Action, Angular momentum

Name of unit	Symbol	Definition	Relation to SI units
SI unit	J·s	≡ kg·m²/s	= 1 J·s
atomic unit of action	au	≡ ℏ = ℎ/2π	≈ 1.054 571 596×10−34 J·s
cgs unit	erg·s		= 10−7 J·s

Electric current

Electric current

Name of unit	Symbol	Definition	Relation to SI units
ampere (SI base unit)	A		1 A
esu per second; statampere (cgs unit)	esu/s	≡ (0.1 A·m/s) /c	≈ 3.335 641×10−10 A
electromagnetic unit; abampere (cgs unit)	abamp		≡ 10 A

Electric charge

Electric charge

Name of unit	Symbol	Definition	Relation to SI units
coulomb (SI unit)	C	≡ A·s	= 1 C
atomic unit of charge	au	≡ e	≈ 1.602 176 462×10−19 C
statcoulomb; franklin; electrostatic unit (cgs unit)	statC; Fr; esu	≡ (0.1 A·m) /c	≈ 3.335 641×10−10 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

Name of unit	Symbol	Definition	Relation to SI units
volt (SI unit)	V	≡ kg·m²/(A·s³)	= 1 V
abvolt (cgs unit)	abV		≡ 1×10−8 V
statvolt (cgs unit)	statV	≡ c· (1 μJ/A·m)	= 299.792 458 V

Electrical resistance

Electrical resistance

Name of unit	Symbol	Definition	Relation to SI units
ohm (SI unit)	Ω	≡ V/A	= kg·m²/(A²·s³)

Inductance

Inductance

Name of unit	Symbol	Definition	Relation to SI units
henry (SI unit)	H	≡ (m²×kg)/(s²×A²) = (V×s)/A = (J×s²)/C² = (m²×kg)/C²	= 1 H

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)	= 1 Pa·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	= 1 m²/s
stokes (cgs unit)	St		≡ 10−4 m²/s

Information entropy

Information entropy

Name of unit	Symbol	Definition	Relation to SI units
SI unit	J/K	≡ 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 (decimal)	kB	≡ 1000 B	= 7.655952(13) × 10−20 J/K
kilobyte (kibibyte)	KB; KiB	≡ 1024 B	= 7.839695(13) × 10−20 J/K

Often, information entropy is measured in shannons, whereas the (discrete) storage space of digital devices is measured in bits. Thus, uncompressed redundant data occupy more than one bit of storage per shannon of information entropy. The multiples of a bit listed above are usually used with this meaning. Other times the bit is used as a measure of information entropy and is thus a synonym of shannon.

Temperature

Note: see Temperature conversion for more detail

Temperature

Name of unit	Symbol	Definition	Relation to SI units
kelvin (SI base unit)	K		1 K
degree Celsius	°C		[K] = [°C] + 273.15
degree Rankine	°R; °Ra		[K] = [°R] × 5⁄9
degree Fahrenheit	°F		[K] = ([°F] + 459.67) × 5⁄9
degree Delisle	°De		[K] = 373.15 − [°De] × 2⁄3
degree Newton	°N		[K] = [°N] × 100⁄33 + 273.15
degree Réaumur	°Ré		[K] = [°Ré] × 5⁄4 + 273.15
degree Rømer	°Rø		[K] = ([°Rø] − 7.5) × 40⁄21 + 273.15

Radioactivity

Radioactivity

Name of unit	Symbol	Definition	Relation to SI units
Becquerel (SI base unit)	Bq	≡ disintegration per second s-1	= 1 Bq
Rutherford	rd	≡ 1 MBq	= 1 * 106 Bq
curie	Ci	≡ 3.7 * 1010 Bq	= 3.7 * 1010 Bq

Radioactivity - absorbed dose

Radioactivity - absorbed dose

Name of unit	Symbol	Definition	Relation to SI units
gray	Gy	≡ 1J/kg = 1m2·s-2	= 1 Gy
rad	rad	≡ 0.01 Gy	= 0.01 Gy

Radioactivity - equivalent dose

Radioactivity - equivalent dose

Name of unit	Symbol	Definition	Relation to SI units
Sievert (SI base unit)	Sv		= 1 Sv
Röntgen equivalent man	rem	≡ 0.01 Sv	= 0.01 Sv

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.
• iMetrix - unit converter for Windows

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

• Units of measurement
• Units conversion by factor-label
• False precision
• Accuracy and precision
• Significant figures
• Approximate conversion of units.
• Temperature conversion formulas for conversions involving additional temperature scales.
• SI
• English unit
• Imperial unit
• U.S. customary unit

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