Definitions

# 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).

### Prefix mnemonic

The phrase King Henry died Monday drinking chocolate milk, with initialism KHD_dcm, is useful for remember the prefixes for every power of ten from 3 to -3. For example, with length in meters: Km, Hm, Dm, m, dm, cm, mm.

## 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 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 ± 3.6 m
barley corn (H)   ≡ ⅓ in (see note above about rounding) ≈ 0.008 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
fermi fm ≡ 1 m = 1 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) ft (US) ≡ 1200/3937 m ≈ 0.304 800 610 m
french; charriere F ≡ 1/3 mm = 3.3  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 (statute) lea ≡ 3 mi = 4828 m
light-day   ≡ 24 light-hours = 2.590 206 837 12 m
light-hour   ≡ 60 light-minutes = 1.079 252 848 8 m
light-minute   ≡ 60 light-seconds = 1.798 754 748 m
light-second   ≡ 2.997 924 58 m
light-year l.y. = 9.460 053 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 m
micron µ ≡ 1 m
mil; thou mil ≡ 1 in = 2.54 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
pace   ≡ 2.5 ft = 0.762 m
palm   ≡ 3 in = 0.0762 m
parsec pc = 3.08567782 ± 6 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)   ≡ 9 in = 0.2286 m
spat ≡ 1012 m = 1×1012 m
stick (H)   ≡ 2 in = 0.05 08 m
pm, stigma, or bicron   ≡ 1 m ≡ 1 m
telegraph mile (H) mi ≡ 6087 ft = 1855.3176 m
twip twp ≡ 1/1440 in = 1.763 8 m
x unit; siegbahn xu ≈ 1.0021 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 = 3.162 ch² = 4046.856 422 4 m²
are a ≡ 100 m²
barn b ≡ 10−28
barony   ≡ 4000 ac = 1.618 742 568 96 m²
board bd ≡ 1 in × 1 ft = 7.741 92 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 m²
circular mil; circular thou circ mil ≡ π/4 mil² ≈ 5.067 075 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 m²
rood ro ≡ ¼ ac = 1011.714 105 6 m²
shed ≡ 10−52
square chain sq ch ≡ 1 sq ch ≡ .10 ac = 404.685 642 24 m²
square foot sq ft ≡ 1 ft × 1 ft = 9.290 304 m²
square inch sq in ≡ 1 in × 1 in = 6.4516 m²
square kilometre km² ≡ 1 km² = 106
square link sq lnk ≡ 1 lnk² = 4.046 856 422 4 m²
square metre (SI unit) ≡ 1 m × 1 m = 1 m²
square mil; square thou sq mil ≡ 1 mil × 1 mil = 6.4516 m²
square mile; section sq mi ≡ 1 mi × 1 mi = 2.589 988 110 336 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 m²
square U.S. Survey mile sq mi ≡ 1 sq mi (US) ≈ 2.589 998 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 m²
yardland   ≡ 30 ac = 1.214 056 926 72 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) ≡ 1 m × 1 m × 1 m = 1 m³
litre L ≡ 1 dm³ = 0.001 m³
lambda λ ≡ 1 mm³ = 1 m³
drop (metric)   ≡ 1/20 mL = 50.0 m³
minim (Imperial) min ≡ 1/480 fl oz (Imp) = 1/60 fl dr (Imp) = 59.193 880 2083  m³
minim (U.S.) min ≡ 1/480 US fl oz = 1/60 US fl dr = 61.611 519 921 875 m³
drop (U.S.) (alt) gtt ≡ 1/456 US fl oz ≈ 64.854 231 m³
drop (Imperial) (alt) gtt ≡ 1/1824 gi (Imp) ≈ 77.886 684 m³
drop (U.S.) gtt ≡ 1/360 US fl oz = 82.148 693 229 16  m³
drop (medical)   ≡ 1/12 ml = 83.03  m³
drop (Imperial) gtt ≡ 1/288 fl oz (Imp) = 98.656 467 0138  m³
dash (U.S.)   ≡ 1/96 US fl oz = ½ US pinch = 308.057 599 609 375 m³
dash (Imperial)   ≡ 1/384 gi (Imp) = ½ pinch (Imp) = 369.961 751 302 08 3  m³
pinch (U.S.)   ≡ 1/48 US fl oz = ⅛ US tsp = 616.115 199 218 75 m³
pinch (Imperial)   ≡ 1/192 gi (Imp) = ⅛ tsp (Imp) = 739.923 502 604 16  m³
fluid scruple (Imperial) fl s ≡ 1/24 fl oz (Imp) = 1.183 877 604 16  m³
fluid drachm (Imperial) fl dr ≡ ⅛ fl oz (Imp) = 3.551 632 812 5 m³
fluid dram (U.S.); U.S. fluidram fl dr ≡ ⅛ US fl oz = 3.696 691 195 312 5 m³
teaspoon (Canadian) tsp ≡ 1/6 fl oz (Imp) = 4.735 510 41 6  m³
teaspoon (U.S.) tsp ≡ 1/6 US fl oz = 4.928 921 595 m³
teaspoon (metric)   ≡ 5.0 m³
teaspoon (Imperial) tsp ≡ 1/24 gi (Imp) = 5.919 388 020 83  m³
dessertspoon (Imperial)   ≡ 1/12 gi (Imp) = 11.838 776 0416  m³
tablespoon (Canadian) tbsp ≡ ½ fl oz (Imp) = 14.206 531 25 m³
tablespoon (U.S.) tbsp ≡ ½ US fl oz = 14.786 764 782 5 m³
tablespoon (metric)   ≡ 15.0 m³
cubic inch cu in ≡ 1 in × 1 in × 1 in = 16.387 064 m³
tablespoon (Imperial) tbsp ≡ 5/8 fl oz (Imp) = 17.758 164 062 5 m³
pony   ≡ 3/4 US fl oz = 22.180 147 171 875 m³
fluid ounce (Imperial) fl oz (Imp) ≡ 1/160 gal (Imp) = 28.413 062 5 m³
fluid ounce (U.S.) US fl oz ≡ 1/128 gal (US) = 29.573 529 562 5 m³
shot   ≡ 1 US fl oz ≈ 29.57 m³
jigger   ≡ 1½ US fl oz ≈ 44.36 m³
gill (U.S.) gi (US) ≡ 4 US fl oz = 118.294 118 25 m³
gill (Imperial); Noggin gi (Imp); nog ≡ 5 fl oz (Imp) = 142.065 312 5 m³
cup (Canadian) c (CA) ≡ 8 fl oz (Imp) = 227.304 5 m³
cup (U.S.) c (US) ≡ 8 US fl oz ≡ 1/16 gal (US) = 236.588 236 5 m³
cup (metric) c ≡ 250.0 m³
breakfast cup   ≡ 10 fl oz (Imp) = 284.130 625 m³
pint (U.S. fluid) pt (US fl) ≡ ⅛ gal (US) = 473.176 473 m³
pint (U.S. dry) pt (US dry) ≡ 1/64 bu (US lvl) ≡ ⅛ gal (US dry) = 550.610 471 357 5 m³
pint (Imperial) pt (Imp) ≡ ⅛ gal (Imp) = 568.261 25 m³
fifth   ≡ 1/5 US gal = 757.082 356 8 m³
quart (U.S. fluid) qt (US) ≡ ¼ gal (US fl) = 946.352 946 m³
quart (U.S. dry) qt (US) ≡ 1/32 bu (US lvl) = ¼ gal (US dry) = 1.101 220 942 715 m³
quart (Imperial) qt (Imp) ≡ ¼ gal (Imp) = 1.136 522 5 m³
pottle; quartern   ≡ ½ gal (Imp) = 80 fl oz (Imp) = 2.273 045 m³
board-foot fbm ≡ 144 cu in = 2.359 737 216 m³
gallon (U.S. fluid; Wine) gal (US) ≡ 231 cu in = 3.785 411 784 m³
gallon (U.S. dry) gal (US) ≡ ⅛ bu (US lvl) = 4.404 883 770 86 m³
gallon (Imperial) gal (Imp) = 4.546 09 m³
beer gallon beer gal ≡ 282 cu in = 4.621 152 048 m³
peck (U.S. dry) pk ≡ ¼ US lvl bu = 8.809 767 541 72 m³
peck (Imperial) pk ≡ 2 gal (Imp) = 9.092 18 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
centesimal second of arc " ≡ 1 grad/10000 ≈ 1.570 796 µrad
arcsecond " ≡ 1°/3600 ≈ 4.848 137 µrad
centesimal minute of arc ' ≡ 1 grad/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
Name of unit Symbol Definition Relation to SI units Relation to avoirdupois units
kilogram, grave kg; G (SI base unit)
electron rest mass, atomic unit of mass me ≈ 9.109 382 15 ± 45 kg
electronvolt eV ≡ 1 eV (energy unit) / c2 = 1.782 6×10−36 kg
unified atomic mass unit u; AMU ≈ 1.660 538 73 ± 13 kg
dalton Da ≈ 1.660 902 10 ± 13 kg
gamma γ ≡ 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) ct ≡ 200 mg
carat kt ≡ 3 1/6 gr ≈ 205.196 548 333 mg
sheet   ≡ 1/700 lb av = 647.9891 mg
scruple (apothecary) s ap ≡ 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 (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.
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   ≡ (G/c5)½ ≈ 1.351 211 818 s
atomic unit of time au a0/(α·c) ≈ 2.418 884 254 s
svedberg S ≡ 10−13 s = 100 fs
shake   ≡ 10−8 s = 10 ns
sigma   ≡ 10−6 s = 1 μs
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 s
lustre; lustrum   ≡ 5 a of 365 d = 1.5768 s
octaeteris   ≡ 8 a of 365 d = 2.522 88 s
decade   ≡ 10 a of 365 d = 3.1536 s
enneadecaeteris; Metonic cycle   ≡ 110 mo (hollow) + 125 mo (full) = 19 a of 365 d = 5.996 16 s
Callippic cycle   ≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d = 2.398 377 6 s
century (Calendar)   ≡ 100 a of 365 d = 3.1536 s
century (Julian)   ≡ 100 a of 365.25 d = 3.155 76 s
Hipparchic cycle   ≡ 4 Callippic cycles - 1 d = 9.593 424 s
millennium (Calendar)   ≡ 1000 a of 365 d = 3.1536 s
millennium (Gregorian)   ≡ 1000 a of 365.2425 d = 3.155 695 2 s
millennium (Julian)   ≡ 1000 a of 365.25 d = 3.155 76 s
Sothic cycle   ≡ 1461 a of 365 d = 4.607 409 6 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 m/s
furlong per fortnight   ≡ furlong/fortnight ≈ 1.663 095 m/s
inch per minute ipm ≡ 1 in/min ≈ 4.23 333 m/s
foot per minute fpm ≡ 1 ft/min = 5.08 m/s
inch per second ips ≡ 1 in/s = 2.54 m/s
kilometre per hour km/h ≡ 1 km/h ≈ 2.777 778 m/s
foot per second fps ≡ 1 ft/s = 3.048 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 ≡ 299 792 458 m/s = 299 792 458 m/s
speed of sound in air s ≈ 344 m/s at 20 °C, 60% relative humidity
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 m/s²
inch per minute per second ipm/s ≡ 1 in/(min·s) ≈ 4.233 333 m/s²
foot per minute per second fpm/s ≡ 1 ft/(min·s) = 5.08 m/s²
galileo Gal ≡ 1 cm/s² = 10−2 m/s²
inch per second squared ips² ≡ 1 in/s² = 2.54 m/s²
foot per second squared fps² ≡ 1 ft/s² = 3.048 m/s²
mile per hour per second mph/s ≡ 1 mi/(h·s) = 4.4704 m/s²
knot per second kn/s ≡ 1 kn/s ≈ 5.144 444 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 m/s²

### Force

Force
Name of unit Symbol Definition Relation to SI units
atomic unit of force ≡ me·α²·c²/a0 ≈ 8.238 722 06 N
dyne (cgs unit) dyn ≡ g·cm/s² = 10−5 N
milligrave-force, gravet-force mGf; gf g × 1 g = 9.806 65 mN
kilogram-force; kilopond; grave-force kgf; kp; Gf g × 1 kg = 9.806 65 N
kip; kip-force kip; kipf; klbf g × 1000 lb = 4.448 221 615 260 5 N
newton (SI unit) N ≡ kg·m/s² = 1 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
poundal pdl ≡ 1 lb·ft/s² = 0.138 254 954 376 N
sthene (mts unit) sn ≡ 1 t·m/s² = 1 N
ton-force tnf g × 1 sh tn = 8.896 443 230 521 N

### 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 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 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 Pa
foot of water (39.2 °F) ftH2O ≈ 999.972 kg/m³ × 1 ft × g ≈ 2.988 98 Pa
inch of mercury (conventional) inHg ≡ 13 595.1 kg/m³ × 1 in × g ≈ 3.386 389 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 Pa
kip per square inch ksi ≡ 1 kipf/sq in ≈ 6.894757 Pa
micron (micrometre) of mercury $mu$mHg ≡ 13 595.1 kg/m³ × 1 $mu$m × g ≈ 0.001 torr ≈ 0. 133 322 4 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 Pa = 1 kPa
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 Pa
short ton per square foot   ≡ 1 sh tn × g / 1 sq ft ≈ 95.760 518 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 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 J
rydberg Ry R··c ≈ 2.179 872 J
hartree Eh ≡ me·α²·c² (= 2 Ry) ≈ 4.359 744 J
atomic unit of energy au ≡ Eh ≈ 4.359 744 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 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 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 J
British thermal unit (ISO) BTUISO ≡ 1.0545 J
British thermal unit (63 °F) BTU63 °F ≈ 1.0546 J
British thermal unit (60 °F) BTU60 °F ≈ 1.054 68 J
British thermal unit (59 °F) BTU59 °F ≡ 1.054 804 J
British thermal unit (International Table) BTUIT = 1.055 055 852 62 J
British thermal unit (mean) BTUmean ≈ 1.055 87 J
British thermal unit (39 °F) BTU39 °F ≈ 1.059 67 J
Celsius heat unit (International Table) CHUIT ≡ 1 BTUIT × 1 K/°R = 1.899 100 534 716 J
cubic foot of atmosphere; standard cubic foot cu ft atm; scf ≡ 1 atm × 1 ft³ = 2.869 204 480 934 4 J
cubic yard of atmosphere; standard cubic yard cu yd atm; scy ≡ 1 atm × 1 yd³ = 77.468 520 985 228 8 J
cubic foot of natural gas   ≡ 1000 BTUIT = 1.055 055 852 62 J
horsepower-hour hp·h ≡ 1 hp × 1 h = 2.684519537696172792 J
kilowatt-hour; Board of Trade Unit kW·h; B.O.T.U. ≡ 1 kW × 1 h = 3.6 J
thermie th ≡ 1 McalIT = 4.1868 J
therm (U.S.)   ≡ 100 000 BTU59 °F = 105.4804 J
therm (E.C.)   ≡ 100 000 BTUIT = 105.505 585 262 J
ton of TNT tTNT ≡ 1 Gcalth = 4.184 J
barrel of oil equivalent bboe ≈ 5.8 ×106 BTU59 °F ≈ 6.12 J
ton of coal equivalent TCE ≡ 7 Gcalth = 29.3076 J
ton of oil equivalent TOE ≡ 10 Gcalth = 41.868 J
quad   ≡ 1015 BTUIT = 1.055 055 852 62 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 W
foot-pound-force per hour ft lbf/h ≡ 1 ft lbf/h ≈ 3.766 161 W
atmosphere cubic centimetre per minute atm ccm ≡ 1 atm × 1 cm³/min = 1.688 75 W
foot-pound-force per minute ft lbf/min ≡ 1 ft lbf/min = 2.259 696 580 552 334 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 W
atmosphere-cubic foot per second atm cfs ≡ 1 atm × 1 cu ft/s = 2.869 204 480 934 4 W
ton of refrigeration (IT)   ≡ 1 BTUIT × 1 sh tn/lb ÷ 10 min/s ≈ 3.516 853 W
ton of refrigeration (Imperial)   ≡ 1 BTUIT × 1 lng tn/lb ÷ 10 min/s ≈ 3.938 875 W
boiler horsepower bhp ≈ 34.5 lb/h × 970.3 BTUIT/lb ≈ 9.810 657 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 = /2π ≈ 1.054 571 596 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 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 C
statcoulomb; franklin; electrostatic unit (cgs unit) statC; Fr; esu ≡ (0.1 A·m) /c ≈ 3.335 641 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 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

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

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

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).

## References

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