Non-SI Units Used in the United States

See the explanatory Notes at the end of the page.


Unit Name Abbrev. Definition Quantity Origin

gal Gal 10 mm/s2 * acceleration 4
mile per hour per second mphps 0.447 04 m/s2 * acceleration 5
standard gravity or free fall g 9.806 65 m/s2 * acceleration 3
second of arc (arc second) " 4.848 137 µrad angle, plane 3
second of right ascension s RA 72.722 05 µrad angle, plane 3
minute of arc (arc minute) ' 290.8882 µrad angle, plane 3
mil (angular) (1/6400 circle) mil 0.981 748 mrad angle, plane 6
minute of right ascension m RA 4.363 323 mrad angle, plane 3
degree (arc degree) o 17.453 29 mrad angle, plane 3
point (compass) (1/32 circle) pt 196.3495 mrad angle, plane 3
hour of right ascension h RA 261.7994 mrad angle, plane 3
revolution (turn) r 6.283 185 rad angle, plane 3
percent grade % equation  angle, plane 3
pitch (roofs)   equation  angle, plane 5
square degree deg2 304.617 42 µsr angle, solid 3
revolution per minute rpm 104.72 mrad/s angular speed 3
revolution per second rps 6.2832 rad/s angular speed 3
barn  b 100 fm2 * area 4
circular mil (π/[0.5 mil]2) cm 506.7075 µm2 area 5
square mil sq mil 645.16 µm2 * area 5
circular inch (π/[0.5 in]2) ? cir in 5.067 075 cm2 area 5
square inch sq in 645.16 mm2 * area 1
square foot sq ft 929.0304 cm2 * area 1
square yard sq yd 0.836 127 4 m2 area 1
square (roofing) (100 ft2) sq 9.29 m2 area 5
acre (commercial) (36 000 ft2) ac 3344.523 m2 area 6
acre (US survey) (43 560 ft2) ac 4046.873 m2 area 1
square mile (International) sq mi 2.589 998 km2 area 1
township twp 93.2 km2 area 6
million acres MMAc 4047 km2 area 6
Dobson unit DU 21.4 mg/m2 areal density 6
"pound" (basis weight of book paper) lb 1.48 g/m2 areal density 5
"pound" (basis weight of newsprint) lb 1.63 g/m2 areal density 5
"pound" (basis weight of cover paper) lb 2.70 g/m2 areal density 5
"pound" (basis weight of bond paper) (sub) lb 3.76 g/m2 areal density 5
ounce per square yard ("ounce") oz 34 g/m2 areal density 5
parts per million ppm 1 mg/L concentration 6
parts per billion ppb 1 µg/L concentration 6
parts per trillion ppt 1 ng/L concentration 6
specific gravity (relative density) sp gr 1 Mg/m3 density 3
degrees Baumé (heavy) ? equation  density 3
degrees Baumé (light) ? equation  density 3
degrees Twaddel ? Two equation  density 3
degrees Bark (tanning liquors) ? oBk equation  density 3
degrees Brix (sugar solutions) ? oBrix equation  density 3
degrees Beck ? oBeck equation  density 3
degrees API (API gravity) (petroleum) G equation  density 6
degrees Soxhlet (milk) ? oSx equation  density 3
degrees Ammoniameter (ammonia) ? oAm equation  density 5
degrees oleometer (vegetable oils) ?   equation  density 5
charge unit e 160.2189 zC electric charge 3
faraday (carbon-12) ?   96.4870 kC electric charge 3
mho   1 S * electric conductance 3
ohm circular mil per foot   1.662 426 nW.m electric resistivity 5
electronvolt eV 160.2189 zJ energy 3
erg erg 100 nJ * energy 4
ounce inch (ounce-force inch) ? ozf.in 7.061 553 mJ energy 5
foot pound (pound-force foot) ft.lb 1.355 818 J energy 5
calorie (thermochemical) cal 4.184 J * energy 4
calorie (international table) cal 4.1868 J * energy 4
liter atmosphere (45o latitude) L.atm 101.3 J energy 4
British thermal unit (thermochemical) Btu 1.054 350 kJ energy 5
British thermal unit (International table) Btu 1.055 056 kJ energy 5
kip foot (1000 lbf.ft) kip.ft 1.356 kJ energy 6
foot ton (ton-force foot) ft.tonf 2.711 636 kJ energy 6
Calorie (nutritional) (ADA) Cal 4.186 kJ * energy 4
horsepower hour hp.h 2.6856 MJ energy 5
ton mile (ton-force mile) tonf.mi 14.32 MJ energy 6
therm (GPA std) th 105.506 MJ energy 5
refrigeration ton (US standard) ? ton 303.9 MJ energy 6
million Btu (International table) MMBtu 1.056 GJ energy 5
ton (nuclear devices) t 4.184 GJ * energy 6
horsepower year hp.yr 23.526 GJ energy 5
metric ton of coal equivalent (UN std) mtce 29.3076 GJ * energy 4
metric ton of oil equivalent (1010 cal)   41.84 GJ * energy 4
quad (Q-unit) Qbtu 1.055 EJ energy 6
Richter magnitude M

equation 

energy 6
gallon (US) per day gpd 43.813 µL/s flow, volumetric 6
cubic inch per minute ? cim 273.1 µL/s flow, volumetric 5
gallon (US) per hour gph 1.0515 mL/s flow, volumetric 6
cubic foot per hour CFH 7.866 mL/s flow, volumetric 5
liter per minute L/min 16.666 mL/s flow, volumetric 4
acre foot per year af/y 39.114 mL/s flow, volumetric 6
gallon (US) per minute gpm 63.09 mL/s flow, volumetric 6
cubic foot per minute cfm 471.95 mL/s flow, volumetric 5
miners inch (ID, KS, NE, NM, NV, SD, UT) ?   566.3 mL/s flow, volumetric 5
miner's inch (AZ, CA, MT, OR)   707.9 mL/s flow, volumetric 5
miners inch (CO) ?   737.4 mL/s flow, volumetric 5
gallon (US) per second gps 3.785 L/s flow, volumetric 6
acre foot per day af/d 14.276 49 L/s flow, volumetric 6
cubic foot per second (cusec, second foot) cfs 28.316 85 L/s flow, volumetric 5
million gallons (US) per day mgd 43.812 64 L/s flow, volumetric 6
dyne dyn 10 µN * force 4
poundal ? pdl 138.255 mN force 5
ounce-force ("ounce") ozf 278.0139 mN force 5
pound-force (“pound”) lbf 4.448 222 N force 5
kilogram-force (“kilogram”) kgf 9.806 65 N * force 4
kip (kilopound-force) (1000 lbf) kip 4.448 222 kN force 6
ton-force (2000 lbf) ("ton") tonf 8.896 kN force 6
footcandle fc 10.764 lx illuminance 4
phot ? ph 10 klx * illuminance 4
exposure value EV equation  illuminance 5
magnitude (apparent stellar) mag equation  intensity 3
decibel (sound level) dB equation  intensity, sound 4
phon   equation  intensity, sound 4
sone   equation  intensity, sound 6
noy ?   equation  intensity, sound 6
langley (cal/cm2) ly 41.84 kJ/m2 * irradiation 6
fermi ?   1 fm * length 4
angstrom Ĺ 100 pm * length 4
microinch µin 25.4 nm * length 6
micron   1 µm * length 4
mil mil 25.4 µm * length 6
caliber (US) cal 254 µm * length 6
point (US printers) pt 351.4598 µm * length 6
point (US computers) pt 352.8 µm length 6
agate (1/14 inch)   1.814 mm length 6
pica (US printers) pca 4.217 518 mm length 6
pica (US computers) pca 4.233 mm length 6
Powerpoint centimeter cm 1.0583 cm length 6
inch in 2.54 cm * length 1
hand   10.16 cm * length 1
link (US survey) (1/100 chain) ? li 20.116 84 cm length 1
foot (International) ft 30.48 cm * length 1
foot (US survey) ft 30.480 061 cm length 1
pace (military) (30 inches)   76 cm length 1
yard yd 91.44 cm * length 1
pace (geometrical) (60 inches)   1.52 m length 1
fathom fm 1.8288 m length 1
rod (US survey) (16.5 survey feet) ? rd 5.029 210 m length 1
chain (US survey) ch 20.116 84 m length 1
cable (US) (100 fathoms) ? ca 182.9 m length 5
furlong fur 201.168 m length 1
"klik" or "K" (slang)   1 km * length 4
mile (International) mi 1.609 344 km * length 1
mile (US survey) mi 1.609 347 km length 1
mile (nautical) NM 1.852 km * length 3
township or range T or R 9.66 km length 6
light second   300 Mm length 3
light minute   18 Gm length 3
astronomical unit AU 149.5979 Gm length 3
light year ly 9.46 Pm length 3
parsec pc 30.857 Pm length 3
American wire gauge awg varies  length 6
Birmingham wire gauge BWG varies  length 6
drill numbers   varies  length 6
nail penny d varies  length 2
screw numbers # varies  length 6
shotgun gauge ga varies  length 5
USS standard plate gauge USS varies  length 6
Washburn & Moen gauge W&M varies  length 6
vinyl gauge ga varies  length 6
men's shoe sizes (US)   equation  length 6
women's shoe sizes (US)   equation  length 6
children's shoe sizes (US)   equation  length 6
denier   0.111 mg/m linear density 4
tex ?   1 mg/m * linear density 4
nit ?   1 cd/m2 * luminance 4
foot-lambert ? ft-L 3.426 cd/m2 luminance 4
lambert ? L 1 lm/cm2 * luminance 4
apparent foot-candle fc 10.76 cd/m2 luminance 4
Einstein unit EU

equation 

luminous energy 4
lumerg ?   1 lm.s * luminous energy 4
lumen hour lm.h 3600 lm.s * luminous energy 4
mean spherical candlepower ? MSCP π/4 lm * luminous flux 4
mean horizontal candlepower ? MHCP   lm luminous flux 4
candlepower (candle) cp 1 cd * luminous intensity 4
oersted ? Oe 79.577 47 A/m magnetic field strength 4
maxwell Mx 10 nWb * magnetic flux 4
unit pole   125.6637 nWb magnetic flux 4
gauss Gs 100 µT * magnetic flux density 4
electron rest mass me 0.000 911 yg mass 3
atomic mass unit (unified) (Dalton) u 1.660 566 yg mass 3
"mig" (slang)   1 mg * mass 4
point (jewelers) pt 2 mg * mass 3
grain gr 64.798 91 mg * mass 1
carat (metric) ct 200 mg * mass 3
pennyweight (troy) dwt 1.555 174 g mass 2
dram (avoirdupois) dr 1.771 845 g mass 1
standard cubic foot (natural gas) scf 20.2 g mass 5
ounce (avoirdupois) oz 28.349 523 g mass 1
assay ton AT 29.167 g mass 6
ounce (troy) ozt 31.103 477 g mass 1
pound (avoirdupois) (poundmass) lb 453.592 37 g * mass 1
bushel (oats) (USDA) bu 14.5 kg mass 6
slug (gee-pound) sl 14.593 90 kg mass 5
bushel (barley) (USDA) bu 21.8 kg mass 6
bushel (shelled corn or rye) (USDA) bu 25.4 kg mass 6
bushel (wheat, soybeans, potatoes)(USDA) bu 27.2 kg mass 6
flask (mercury)   34.5 kg mass 5
hundredweight (short or net) cwt 45.4 kg mass 6
barrel (petroleum) bbl 135 kg mass 6
ton (short or net) tn 907.185 kg mass 6
metric ton t 1 Mg * mass 4
ton (long, gross, or displacement) T 1016 kg mass 1
body mass index BMI 1 kg/m2 * mass per height squared 4
Btu per hour (international table) BTUH 293 mW power 5
horsepower (mechanical) hp 745.7 W power 5
refrigeration ton (US com'l) (200 Btu/min)   3.517 kW power 6
solar luminosities   383 YW power 3
energy efficiency ratio ([Btu/h]/W) EER

0.293

W/W power ratio 6
feet of air ?   3.656 Pa pressure 5
millimeters of water mmH2O 9.8064 Pa pressure 4
pound-force per square foot psf 47.88 Pa pressure 5
millibar mb 100 Pa * pressure 4
millimeter of mercury mmHg 133.322 Pa pressure 4
inch of water (60 oF) "WC 248.84 Pa pressure 5
ounce-force per square inch ozi 430.922 Pa pressure 5
foot of water (39.2 oF) ftWC 2.988 98 Pa pressure 5
inch of mercury (60 oF) inHg 3.376 85 kPa pressure 5
pound-force per square inch psi 6.894 757 kPa pressure 5
atmosphere (standard) atm 101.325 kPa * pressure 4
kip per square inch ksi 6.894 757 MPa pressure 6
decibel (sound pressure level) dB

equation 

pressure 4
rad rd 10 mGy * radiation absorbed dose 4
rem R 10 µSv * radiation dose equivalent 4
roentgen R 258 µC/kg radiation exposure 4
curie Ci 37 GBq * radioactivity 4
neper Np

equation 

ratio 3
foot per hour ? fph 84.66 µm/s speed 5
inch per minute ? ipm 423.3 µm/s speed 5
foot per minute fpm 5.08 mm/s * speed 5
inch per second ips 25.4 mm/s * speed 5
kilometer per hour kph 0.2777 m/s speed 4
foot per second fps 0.3048 m/s * speed 5
mile per hour mph 0.447 m/s speed 5
knot kt 0.514 m/s speed 3
mile per minute mpm 26.82 m/s speed 5
Mach number mach

equation 

speed 3
mile per second mps 1.609 km/s speed 5
speed of light c 299.792 458 Mm/s * speed 3
degrees Fahrenheit oF equation  temperature 5
degrees Rankine oR equation  temperature 5
R-value R 0.1761 K.m2/W thermal insulance 6
radar nautical mile ?   12.261 µs time 6
second (sidereal) s 0.997 269 6 s time 3
minute (sidereal) m 59.836 17 s time 3
minute (solar) min 60 s * time 3
hour (sidereal) h 3.590 170 ks time 3
hour (solar) h 3.6 ks * time 3
day (sidereal) d 86.164 09 ks time 3
day (solar) d 86.4 ks * time 3
week (work, 40 h) wk 144 ks time 3
week (calendar) wk 604.8 ks time 3
month (sidereal) mo 2.360 591 Ms time 3
month (synodic or lunar) mo 2.551 443 Ms time 3
month (mean calendar) mo 2.63 Ms time 3
year (lunar)   30.617 309 Ms time 3
year (common calendar, 365 d) yr 31.536 001 Ms time 3
year (tropical or seasonal) a 31.556 926 Ms time 3
year (sidereal)   31.558 150 Ms time 3
year (anomalistic)   31.558 430 Ms time 3
year (leap calendar, 366 d)   31.622 401 Ms time 3
decade   315.6 Ms time 3
century   3.156 Gs time 3
millennium   31.56 Gs time 3
dyne centimeter dyn.cm 0.1 µN.m * torque 4
"ounce-inch" (ounce-force inch) oz-in 7.061 mN.m torque 5
"inch-pound" (pound-force inch) in-lb 113 mN.m torque 6
foot pound (pound-force foot) ft.lb 1.356 N.m torque 5
centipoise cp 1 mPa.s * viscosity, absolute 4
API "weight" (petroleum)  

equation 

viscosity, absolute 6
reyn (lbf.s/in2) ?   6.894 76 kPa.s viscosity, absolute 5
gallon (US) per day per square foot gpd/sf 0.144 mm2/s viscosity, kinematic 6
stokes (cm2/s) st 0.0001 m2/s viscosity, kinematic 4
saybolt second ?   ?   viscosity, kinematic 6
redwood second ?   ?   viscosity, kinematic 6
drop gtt 50 µL * volume 6
minim (US) ?   61.61 µL volume 1
"mill" or "cc" (slang)   1 mL * volume 4
teaspoon (US) tsp 5 mL volume 1
tablespoon (US) Tbsp 15 mL volume 1
cubic inch cu in 16.387 064 mL * volume 1
fluid ounce (US) ("shot") fl oz 29.574 mL volume 6
jigger (US) (1.5 fl oz) ji 44 mL volume 6
cup (US) C 240 mL volume 6
pint (US liquid) pt 473.2 mL volume 1
pint (US dry) pt 550.6 mL volume 1
bottle (wine)   750 mL * volume 4
quart (US liquid) qt 946.4 mL volume 1
liters per flush Lpf 1 L * volume 6
quart (US dry) qt 1.101 L volume 1
magnum   1.5 L * volume 4
board foot bf 2.36 L volume 1
gallon (US liquid) gal 3.785 L volume 1
peck (US dry) pk 8.81 L volume 1
flat (strawberries) (24 US dry pints)   13.2 L volume 6
sack (bag) (1/6 US dry bbl)   19.3 L volume 6
cubic foot cu ft 28.316 847 L volume 1
standard cubic foot (natural gas) scf 28.328 L volume 6
keg (US small beer) (1/4 US fed bbl)   29.3 L volume 1
bushel (US volume) (2150.42 in3) bu 35.239 L volume 1
keg (US large beer) (1/2 US fed bbl)   58.7 L volume 1
barrel (US cranberry) (5826.5 in3) ? bbl 95.5 L volume 6
barrel (US dry) (105 US dry qt) bbl 115.628 L volume 1
barrel (US federal) (31 US gal) bbl 117.348 L volume 1
barrel (US liquid) (31.5 US gal) bbl 119.24 L volume 1
barrel (US federal proof spirits) (40 US gal) ? bbl 151.416 L volume 1
barrel (petroleum) (42 US gal) bbl 158.99 L volume 6
drum (55 US gallons)   208.4 L volume 6
cord foot (16 ft3) cd-ft 453 L volume 1
cubic yard (27 ft3) cy 764.6 L volume 2
freight ton (40 ft3)   1.1327 m3 volume 2
thousand board feet Mbf 2.36 m3 volume 6
register ton (100 ft3) ton, CCF 2.832 m3 volume 5
cord (128 ft3) cd 3.63 m3 volume 2
acre inch (3630 ft3) ac-in 102.79 m3 volume 6
acre foot (43 560 ft3) af 1233.5 m3 volume 6
million barrels (petroleum) MMbbl 158 987 m3 volume 6
million cubic yards MMcy 0.765 hm3 volume 6
thousand acre feet Maf 1.233 hm3 volume 6
billion cubic feet Bcf 28.317 hm3 volume 6
million board feet MMbf 2360 m3 volume 6
million acre feet maf 1233 km3 volume 6
cubic mile mi3 4.168 km3 volume 5
trillion cubic feet Tcf 28.317 km3 volume 6

Unit Name Abbrev.

Definition

Quantity Origin

 
Notes

Unit name

The current status of units followed by ? is uncertain; some may no longer be in use.

Names in quotes are slang expressions.

Units Included:

  1. Individual non-SI units used in the United States today, regardless of origin.
  2. Compound (derived) units with special names or abbreviations (e.g., psi, cfs, gpm).
  3. Old units no longer in widespread use but still common in some fields (e.g., hand, furlong, grain).
  4. Gauges used as units, even if the increment is not consistent (e.g., AWG, USS ga).
  5. Non-linear scales used as units (e.g., Richter magnitude).

Units Excluded:

  1. Compound units without special names or abbreviations (e.g., cal/s, ft/s2).
  2. Obsolete units found only in historical sources (e.g., scruple, dry gallon, troy pound, cubit).
  3. Prefixed multiples (e.g., milligal, kilobar), unless prefixes are not normal with that unit (e.g., microinch, kilopound).

Abbreviation

Commonly used abbreviations are shown, even when they are not correct or logical. For some units, there are many variations, especially regarding capitalization, not all of which can be indicated here.

Definition

The definition is given in SI units.

Exact definitions are followed by an asterisk (*). All others are rounded to an appropriate precision.

Equation means the unit is defined by an equation (not shown owing to lack of space).

Varies means the unit is a "gauge" system that varies slightly in size, so no single conversion factor can be given.

Quantity

The most common name of the quantity measured by the unit. (Some quantities have several alternative names, not shown.)

Origin

Most non-SI units have multiple origins and complex, often obscure histories.

However, an attempt has been made to assign each unit to one of the following categories, based on its earliest use, although the exact value may have changed slightly due to imprecise standards.

  1. Medieval English version (before 1700) of old European unit (origin Greek, Roman, French, Germanic, etc.).
  2. Medieval English invention (no precedent in other countries).
  3. World customary or scientific (neither metric nor exclusively "English").
  4. Metric (non-SI), including metric-English hybrids, regardless of country of origin.
  5. British scientific/industrial; non-metric, after 1700 (includes a few that originated on the Continent or possibly U.S.)
  6. U.S. invention (non-metric, after 1800), including business, industry, and scientific units.

[Top of this page]

© 2000-2004, WFP Consulting and Dennis Brownridge