This article gives a list of conversion factors for several physical quantities. A number of different units (some only of historical interest) are shown and expressed in terms of the corresponding SI unit. Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10−6 metre). Within each table, the units are listed alphabetically, and the SI units (base or derived) are highlighted.
The following quantities are considered: length, area, volume, plane angle, solid angle, mass, density, time, frequency, velocity, volumetric flow rate, acceleration, force, pressure (or mechanical stress), torque (or moment of force), energy, power (or heat flow rate), action, dynamic viscosity, kinematic viscosity, electric current, electric charge, electric dipole, electromotive force (or electric potential difference), electrical resistance, capacitance, magnetic flux, magnetic flux density, inductance, temperature, information entropy, luminous intensity, luminance, luminous flux, illuminance, radiation.
+ Legend Symbol Definition ≡ exactly equal ≈ approximately equal to ≘ (exactly) corresponds to (different types of quantity describing the same phenomenon) indicates that digits repeat infinitely (e.g. corresponds to ) (H) of chiefly historical interest
Length + LengthName of unitSymbolDefinitionRelation to SI units ångström Å ≡ ≡ 0.1 nm astronomical unit au ≡ ≈ Distance from Earth to Sun ≡ attometre am ≡ ≡ barleycorn (H) = in (see note above about rounding) = 8.4 m bohr, atomic unit of length a0 = Bohr radius of hydrogen ≈ "NIST Reference on Constants, Units, and Uncertainty."(2010). National Institute of Standards and Technology. Retrieved October 17, 2014. cable length (imperial) ≡ 608 ft ≈ 185.3184 m cable length (International) ≡ nmi ≡ 185.2 m cable length (US) ≡ 720 ft = 219.456 m chain (Gunter's; Surveyor's) ch ≡ 66 ft (US) ≡ 4 rods ≈ cubit (H) ≡ Distance from fingers to elbow ≈ 18 in ≈ 0.5 m ell (H) ell ≡ 45 in Lide, D. (Ed.). (1990). Handbook of Chemistry and Physics (71st ed). Boca Raton, FL: CRC Press. Section 1. (In England usually) = 1.143 m fathom ftm ≡ 6 ft = 1.8288 m femtometre fm ≡ ≡ fermi fm ≡ ≡ finger ≡ in = finger (cloth) ≡ in = 0.1143 m foot (Benoît) (H) ft (Ben) ≈ foot (Cape) (H) Legally defined as 1.033 English feet in 1859 ≈ foot (Clarke's) (H) ft (Cla) ≈ foot (Indian) (H) ft Ind ≈ foot, metric mf ≡ 300 mm ≡ 0.3 m foot, metric (Mesures usuelles) (H) ≡ m ≡ 0. m foot (International) ft ≡ 0.3048 m ≡ yd ≡ 12 inches ≡ 0.3048 m foot (Sear's) (H) ft (Sear) ≈ foot (US Survey) ft (US) ≡ m National Bureau of Standards. (June 30, 1959). Refinement of values for the yard and the pound. Federal Register, viewed September 20, 2006 at National Geodetic Survey web site. ≈ french; charriere F ≡ mm = 0. m furlong fur ≡ 10 chains = 660 ft = 220 yd = 201.168 m hand ≡ 4 in ≡ 0.1016 m inch (International) in ≡ 2.54 cm ≡ yd ≡ ft ≡ 0.0254 m league (land) lea ≈ 1 hour walk, Currently defined in US as 3 Statute miles, but historically varied from 2 to 9 km ≈ light-day ≡ 24 light-hours ≡ light-hour ≡ 60 light-minutes ≡ light-minute ≡ 60 light-seconds ≡ light-second ≡ Distance light travels in one second in vacuum ≡ light-year ly ≡ Distance light travels in vacuum in 365.25 days ≡ line ln ≡ in Klein, Herbert Arthur. (1988). The Science of Measurement: a Historical Survey. Mineola, NY: Dover Publications 0-4862-5839-4. = m link (Gunter's; Surveyor's) lnk ≡ ch ≡ 0.66 ft (US) ≡ 7.92 in ≈ link (Ramsden's; Engineer's) lnk ≡ 1 ft = 0.3048 m metre (SI base unit)(meter) m ≡ Distance light travels in of a second in vacuum. (SI base unit) mickey ≡ in = micrometre (old: micron) μ; μm ≡ ≡ mil; thou mil ≡ = mil (Sweden and Norway) mil ≡ 10 km = mile (geographical) (H) ≡ = mile (international) mi ≡ 80 chains ≡ ≡ ≡ mile (tactical or data) ≡ ≡ mile (telegraph) (H) mi ≡ = mile (US Survey) mi ≡ US Survey feet ≡ ( × ) m ≈ nail (cloth) ≡ in = nanometre nm ≡ ≡ nautical league NL; nl ≡ 3 nmi = nautical mile (Admiralty) NM (Adm);nmi (Adm) = = nautical mile (international) NM; nmi ≡ International System of Units, 8th ed. (2006), Bureau International des Poids et Mesures, Section 4.1 Table 8. ≡ nautical mile (US pre 1954) ≡ 1853.248 m ≡ 1853.248 m pace ≡ 2.5 ft = 0.762 m palm ≡ 3 in = 0.0762 m parsec pc Distant point with a parallax shift of one arc second from a base of one astronomical unit. ≡ au ≈ P. Kenneth Seidelmann, Ed. (1992). Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books. p. 716 and s.v. parsec in Glossary. pica ≡ 12 points Dependent on point measures. picometre pm ≡ ≡ point (American, English)Whitelaw, Ian. (2007). A Measure of All Things: The Story of Man and Measurement. New York: Macmillan 0-312-37026-1. p. 152.De Vinne, Theodore Low (1900). The practice of typography: a treatise on the processes of type-making, the point system, the names, sizes, styles and prices of plain printing types 2nd ed. New York: The Century Co. p. 142–150. pt ≡ in ≈ point (Didot; European) Pasko, Wesley Washington (1894). American dictionary of printing and bookmaking. (1894). New York: Howard Lockwood. p. 521. pt ≡ × of pied du roi;After 1878:≡ cm ≈ ;After 1878:≈ point (PostScript) pt ≡ in = m point (TeX) pt ≡ in = 0.00 m quarter ≡ yd = 0.2286 m rod; pole; perch (H) rd ≡ ft = 5.0292 m rope (H) rope ≡ 20 ft = 6.096 m shaku (Japan) ≡ 10/33 m ≈ 0.303 0303 m span (H) ≡ 9 in = 0.2286 m spat ≡ stick (H) ≡ 2 in = 0.0508 m soot ≡ 1/8 in = 0.0031 m toise (French, post 1667) (H) T ≡ 27000/13853 m ≈ 1.949 0363 m twip twp ≡ in = 1.763 m x unit; siegbahn xu ≈ m yard (International) yd ≡ 0.9144 m ≡ 3 ft ≡ 36 in ≡ 0.9144 m yoctometre ym ≡ ≡ zeptometre zm ≡ ≡
Area + AreaName of unitSymbolDefinitionRelation to SI units acre (international) ac ≡ = ≡ acre (US survey) ac ≡ 10 sq ch = , also ≈ Thompson, A. and Taylor, B.N. (2008). Guide for the Use of the International System of Units (SI). National Institute of Standards and Technology Special Publication 811. p. 57. are a ≡ 100 m2 ≡ 100 m2 barn b ≡ 10−28 m2 ≡ 10−28 m2 barony ≡ ac ≡ board bd ≡ ≡ boiler horsepower equivalent direct radiation bhp EDR ≡ 1 ft2 × 1 bhp / (240 BTUIT/h) ≈ circular inch circ in ≡ sq in ≈ circular mil; circular thou circ mil ≡ mil2 ≈ cord ≡ 192 bd ≡ cuerda (PR Survey) cda ≡ 1 cda x 1 cda = acre ≡ dunam ≡ ≡ guntha (India) ≡ 121 sq yd ≈ 101.17 m2 hectare ha ≡ ≡ hide ≈ 120 ac (variable) ≈ rood ro ≡ ac = ping ≡ m × m ≈ section ≡ = shed ≡ 10−52 m2 = 10−52 m2 square (roofing) ≡ = square chain (international) sq ch ≡ = ac ≡ square chain (US Survey) sq ch ≡ = US survey acre ≈ square foot sq ft ≡ ≡ square foot (US Survey) sq ft ≡ ≈ square inch sq in ≡ ≡ square kilometre km2 ≡ 1 km × 1 km = 106 m2 square link (Gunter's)(International) sq lnk ≡ 1 lnk × 1 lnk ≡ 0.66 ft × 0.66 ft = square link (Gunter's)(US Survey) sq lnk ≡ ≡ ≈ square link (Ramsden's) sq lnk ≡ 1 lnk × 1 lnk ≡ 1 ft × 1 ft = square metre (SI unit) m2 ≡ 1 m × 1 m = 1 m2 square mil; square thou sq mil ≡ 1 mil × 1 mil = square mile sq mi ≡ 1 mi × 1 mi ≡ square mile (US Survey) sq mi ≡ 1 mi (US) × 1 mi (US) ≈ square rod/pole/perch sq rd ≡ 1 rd × 1 rd = square yard (International) sq yd ≡ 1 yd × 1 yd ≡ stremma ≡ = township ≡ 36 sq mi (US) ≈ yardland ≈ 30 ac ≈
Volume + VolumeName of unitSymbolDefinitionRelation to SI units acre-foot ac ft ≡ 1 ac x 1 ft = = acre-inch ≡ 1 ac × 1 in = barrel (imperial) bl (imp) ≡ 36 gal (imp) = barrel (petroleum); archaic blue-barrel bl; bbl ≡ 42 gal (US) ≡ barrel (US dry) bl (US) ≡ 105 qt (US) = 105/32 bu (US lvl) = barrel (US fluid) fl bl (US) ≡ gal (US) = board-foot bdft ≡ 144 in3 ≡ bucket (imperial) bkt ≡ 4 gal (imp) = bushel (imperial) bu (imp) ≡ 8 gal (imp) = bushel (US dry heaped) bu (US) ≡ bu (US lvl) = bushel (US dry level) bu (US lvl) ≡ = butt, pipe ≡ 126 gal (US) (wine) = coomb ≡ 4 bu (imp) = cord (firewood) ≡ = cord-foot ≡ 16 ft3 = cubic fathom cu fm ≡ 1 fm × 1 fm × 1 fm = cubic foot cu ft or ft3 ≡ 1 ft × 1 ft × 1 ft ≡ cubic inch cu in or in3 ≡ 1 in × 1 in × 1 in ≡ cubic metre (SI unit) m3 ≡ 1 m × 1 m × 1 m ≡ 1 m3 cubic mile cu mi or mi3 ≡ 1 mi × 1 mi × 1 mi ≡ cubic yard yd3 ≡ 27 ft3 ≡ cup (breakfast) ≡ 10 fl oz (imp) = cup (Canadian) c (CA) ≡ 8 fl oz (imp) = cup (metric) c ≡ ≡ cup (US customary) c (US) ≡ 8 US fl oz ≡ gal (US) = cup (US food nutrition labeling) c (US) ≡ 240 mL = dash (imperial) ≡ gi (imp) = 1/8 tsp (imp) = m3 dash (US) ≡ US fl oz = 1/8 US tsp = dessertspoon (imperial) ≡ gi (imp) = m3 drop (imperial) gtt ≡ fl oz (imp) = m3 drop (imperial) (alt) gtt ≡ gi (imp) ≈ drop (medical) ≡ mL = 83. m3 drop (metric) ≡ mL = drop (US) gtt ≡ US fl oz = m3 drop (US) (alt) gtt ≡ US fl oz ≈ drop (US) (alt) gtt ≡ US fl oz ≈ fifth ≡ US gal = firkin ≡ 9 gal (imp) = fluid drachm (imperial) fl dr ≡ fl oz (imp) = fluid dram (US); US fluidram fl dr ≡ US fl oz = fluid scruple (imperial) fl s ≡ fl oz (imp) = m3 gallon (beer) beer gal ≡ 282 in3 = gallon (imperial) gal (imp) ≡ ≡ gallon (US dry) gal (US) ≡ bu (US lvl) = gallon (US fluid; Wine) gal (US) ≡ 231 in3 ≡ gill (imperial); Noggin gi (imp); nog ≡ 5 fl oz (imp) = gill (US) gi (US) ≡ 4 US fl oz = hogshead (imperial) hhd (imp) ≡ 2 bl (imp) = hogshead (US) hhd (US) ≡ 2 fl bl (US) = jigger (bartending) ≡ US fl oz ≈ kilderkin ≡ 18 gal (imp) = lambda λ ≡ 1 mm3 = last ≡ 80 bu (imp) = litre(liter) L or l ≡ 1 dm3 Barry N. Taylor, Ed.,NIST Special Publication 330: The International System of Units (SI) (2001 Edition), Washington: US Government Printing Office, 43,"The 12th Conference Generale des Poids et Mesures (CGPM)...declares that the word "litre" may be employed as a special name for the cubic decimetre". ≡ 0.001 m3 load ≡ 50 ft3 = minim (imperial) min ≡ fl oz (imp) = 1/60 fl dr (imp) = m3 minim (US) min ≡ US fl oz = US fl dr = ounce (fluid imperial) fl oz (imp) ≡ gal (imp) ≡ ounce (fluid US customary) US fl oz ≡ gal (US) ≡ ounce (fluid US food nutrition labeling) US fl oz ≡ 30 mL ≡ peck (imperial) pk ≡ 2 gal (imp) = peck (US dry) pk ≡ US lvl bu = perch per ≡ = pinch (imperial) ≡ gi (imp) = dash (imp) = m3 pinch (US) ≡ US fl oz = US dash = pint (imperial) pt (imp) ≡ gal (imp) = pint (US dry) pt (US dry) ≡ bu (US lvl) ≡ gal (US dry) = pint (US fluid) pt (US fl) ≡ gal (US) = pony ≡ US fl oz = pottle; quartern ≡ gal (imp) = 80 fl oz (imp) = quart (imperial) qt (imp) ≡ gal (imp) = quart (US dry) qt (US) ≡ bu (US lvl) = gal (US dry) = quart (US fluid) qt (US) ≡ gal (US fl) = quarter; pail ≡ 8 bu (imp) = register ton ≡ 100 ft3 = sack (US) ≡ 3 bu (US lvl) = seam ≡ 8 bu = shot (US) usually 1.5 US fl oz ≈ strike (imperial) ≡ 2 bu (imp) = strike (US) ≡ 2 bu (US lvl) = tablespoon (Australian metric) ≡ tablespoon (Canadian) tbsp ≡ fl oz (imp) = tablespoon (imperial) tbsp ≡ fl oz (imp) = tablespoon (metric) ≡ tablespoon (US customary) tbsp ≡ US fl oz = tablespoon (US food nutrition labeling) tbsp ≡ 15 mL = teaspoon (Canadian) tsp ≡ fl oz (imp) = m3 teaspoon (imperial) tsp ≡ gi (imp) = m3 teaspoon (metric) ≡ ≡ teaspoon (US customary) tsp ≡ US fl oz = teaspoon (US food nutrition labeling) tsp ≡ 5 mL = timber foot ≡ 1 ft3 = ton (displacement) ≡ 35 ft3 = ton (freight) ≡ 40 ft3 = ton (water) ≡ 28 bu (imp) = tun ≡ 252 gal (wine) = wey (US) ≡ 40 bu (US lvl) =
Plane angle + Plane angleName of unitSymbolDefinitionRelation to SI units NATO mil (various) ≡ rad ≈ Swedish streck ≡ rad ≈ milliradian mrad ≡ rad ≈ Warsaw Pact mil ≡ rad ≈ arcminute; MOA ' ≡ ≈ arcsecond " ≡ ≈ centesimal minute of arc ' ≡ grad ≈ centesimal second of arc " ≡ grad ≈ degree (of arc) ° ≡ of a revolution ≡ rad ≈ grad; gradian; gon grad ≡ of a revolution ≡ rad ≡ 0.9° octant ≡ 45° ≈ quadrant ≡ 90° ≈ radian (SI unit) rad The angle subtended at the center of a circle by an arc whose length is equal to the circle's radius.One full revolution encompasses 2π radians. = 1 rad sextant ≡ 60° ≈ sign ≡ 30° ≈