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All conversions are based on the definitions, assumptions and the values of standard variables presented below.
GENERAL
Variable
|
Value
|
Meaning
|
Notes
|
StandardGravity
|
9.80665
|
Standard acceleration due to gravity is 9.80665 m/s2
|
Exact definition
|
LENGTH
Variable
|
Value
|
Meaning
|
Notes
|
OneFootEqualsInches
|
12
|
1 ft = 12 in
|
Exact definition
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OneInchEqualsMeters
|
0.0254
|
1 in = 0.0254 m
|
Exact definition
|
OneYardEqualsMeters
|
0.9144
|
1 yard = 91.44 cm
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Exact definition
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OneLandMileEqualsYards
|
1760
|
1 land mile = 1760 yards
|
Exact definition
|
OneNauticalMileEqualsMeters
|
1852
|
1 nautical mile = 1852 m
|
Exact definition
|
OneAngstromEqualsMeters
|
0.0000000001
|
1 angstrom = 10-10 m
|
Exact definition
|
OneLightYearEqualsMeters
|
9460730472580800
|
1 light-year = 9,460,730,472,580,800 m
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Exact definition
|
OneAstronomicalUnitEqualsMeters
|
149597870700
|
1 AU = 149,597,870,700 m
|
Exact definition
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OneFathomEqualsFeet
|
6
|
1 fathom = 6 feet
|
Exact definition
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OneChainEqualsFeet
|
66
|
1 chain (ch) = 66 feet
|
Exact definition
|
OneParsecEqualsAU
|
648000 / π
|
1 parsec = 648000/π Astronomical Units
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Exact definition
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AREA
Variable
|
Value
|
Meaning
|
Notes
|
OneSquareMetreEqualsBarns
|
10^28
|
1 m2 = 1028 barn (1 barn = 10-28 m2)
|
Exact definition
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OneStremmaEqualsSquareMeters
|
1000
|
1 stremma = 1000 m2
|
Exact definition
|
OneSqMileEqualsAcres
|
640
|
1 square mile = 640 acres
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Exact definition
|
MASS (and FORCE)
Variable
|
Value
|
Meaning
|
Notes
|
OneLbmEqualsKg
|
0.45359237
|
1 lbm (avoirdupois) = 0.45359237 kg
|
Exact definition
|
OneGrainEqualsmg
|
64.79891
|
1 grain = 64.79891 milligrams
|
Exact definition
|
OneTroyOunceEqualskg
|
0.0311034768
|
1 troy ounce (ozt) = 0.0311034768 kg
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Exact definition
|
OneLongTonEqualsGrams
|
1016046.9088
|
1 long ton = 1,016,046.9088 grams
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Exact definition
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OneShortTonEqualsLbm
|
2000
|
1 short ton = 2000 lbm
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Exact definition
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OneOunceEqualsGram
|
28.349523125
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1 ounce (avoirdupois) = 28.349523125 g
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Exact definition
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OnePennyweightEqualsGrains
|
24
|
1 pennyweight = 24 grains
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Exact definition
|
TIME
Variable
|
Value
|
Meaning
|
Notes
|
OneMinuteEqualsSeconds
|
60
|
1 min = 60 s
|
Exact definition
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OneHourEqualsMinutes
|
60
|
1 hour = 60 min
|
Exact definition
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OneDayEqualsHours
|
24
|
1 day = 24 h
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Conventional civil definition
|
OneWeekEqualsDays
|
7
|
1 week = 7 days
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Exact definition
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OneJulianYearEqualsDays
|
365.25
|
1 Julian year = 365.25 days
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Exact definition
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OneCommonYearEqualsDays
|
365
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1 Common year = 365 days
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Calendar definition
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OneDecadeEqualsYears
|
10
|
1 decade = 10 years
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Conventional definition
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OneCenturyEqualsYears
|
100
|
1 century = 100 years
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Conventional definition
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VOLUME
Variable
|
Value
|
Meaning
|
Notes
|
OneImperialGallonEqualsLitres
|
4.54609
|
1 imperial gallon = 4.54609 litres
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Exact definition, by UK law
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OneUSGallonEqualsCubicInches
|
231
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1 US gallon = 231 cubic inches
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Exact definition, by US NIST standards
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OneImperialPintEqualsImperialFluidOunces
|
20
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1 imperial pint = 20 imperial fluid ounces
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Exact definition
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OneUSPintEqualsUSFluidOunces
|
16
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1 US pint = 16 US fluid ounces
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Exact definition
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OneGallonEqualsPints
|
8
|
1 gallon = 8 pints *
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Exact definition
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OneGallonEqualsQuarts
|
4
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1 gallon = 4 quarts *
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Exact definition
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OneFluidOunceEqualsMinims
|
480
|
1 fluid ounce = 480 minims *
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Exact definition
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OneFluidOunceEqualsFluidDrams
|
8
|
1 fluid ounce = 8 fluid drams *
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Exact definition
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OneTroyPoundEqualsTroyOunces
|
12
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1 troy pound = 12 troy ounces
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Exact definition
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* Applies to both imperial and US units (gallon, pint, quart, fluid ounce, minim, etc).
SPEED
Variable
|
Value
|
Meaning
|
Notes
|
SpeedOfLightInMeterPerSecond
|
299792458
|
c = 299,792,458 m/s
|
Exact definition
According to the 1983 definition and the 2019 revision of the SI base units.
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PRESSURE
Variable
|
Value
|
Meaning
|
Notes
|
OneBarEqualsPascal
|
100000
|
1 bar = 100000 Pa
|
Exact definition
|
OnemmHgEqualsPascal
|
133.322387415
|
1 mm of mercury = 133.322387415 Pa
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Conventional value
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OneStandardAtmosphereEqualsPascal
|
101325
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1 standard atmosphere = 101,325 Pa
|
Exact definition
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OneAtmosphereEqualsTorr
|
760
|
1 standard atmosphere = 760 Torr
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Exact definition
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COMPUTER
Variable
|
Value
|
Meaning
|
Notes
|
OneByteEqualsBits
|
8
|
1 byte = 8 bits
|
Exact definition
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ENERGY
Variable
|
Value
|
Meaning
|
Notes
|
OneFoeEqualsJoules
|
10^44
|
1 foe = 1044 J
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Exact definition
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OneThermEqualsBTU
|
10^5
|
1 therm = 100,000 BTU
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Exact definition for US therm, defined by US standards.
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OneCalTHEqualsJoules
|
4.184
|
1 thermochemical calorie = 4.1840 J
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Exact definition, set in 1956.
|
OneCalITEqualsJoules
|
4.1868
|
1 Int. Steam Table calorie (1956) = 4.1868 J
|
Exact definition
The Fifth International Conference on the Properties of Steam (London, July 1956) defined the International Table calorie as 4.1868 J
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OneCal15EqualsJoules
|
4.1855
|
One 15 °C calorie ≈ 4.1855 J
|
This is not an exact definition but an experimentally determined value.
The amount of energy required to warm one gram of air-free water from 14.5 to 15.5 °C at standard atmospheric pressure. Experimental values of this calorie ranged from 4.1852 to 4.1858 J. The CIPM in 1950 (Comité international des poids et mesures (International Committee for Weights and Measures) 1950; PV, 1950, 22, 79–80) published a mean experimental value of 4.1855 J, noting an uncertainty of 0.0005 J.
|
OneTonOfTNTEqualsCaloriesTH
|
10^9
|
1 ton TNT ≈ 109 thermochemical calories
|
Common approximation used in physics and engineering. Not an exact physical constant.
|
OneBTUITEqualsJoules
|
OneLbmEqualsKg * 1000 * 5 / 9 * OneCalITEqualsJoules = 1055.05585262
|
1 BTU(IT) = 1055.05585262 J
|
Based on the International Table calorie (1956), defined as 4.1868 J. This is the standard BTU used in engineering.
The most widespread BTU uses the International Steam Table (IT) calorie, which was defined by the Fifth International Conference on the Properties of Steam (London, July 1956) to be exactly 4.1868 J. Therefore, the exact conversion factor for the International Table Btu is 1055.05585262 J, as shown in the calculation.
|
OneBTUTHEqualsJoules
|
OneLbmEqualsKg * 1000 * 5 / 9 * OneCalTHEqualsJoules = 9489.1523804 / 9 ≈ 1054.350264488889
|
1 BTU(TH) = 9489.1523804 / 9 J ≈ 1054.350264488889 J
|
Conventional value, not exact.
It is based on the definition of the thermochemical calorie, which is equal to 4.184 J. The calculation is similar to the one for the IT case.
|
OneBTU59FEqualsJoules
|
1054.804
|
1 BTU(59) = 1054.804
|
Conventional value, not exact.
59 °F (15 °C) is the most widely used reference temperature for BTU definition in the US.
Different values can be found in the literature. This value is the one most commonly used. See:
https://en.wikipedia.org/wiki/British_thermal_unit (reporting 1054.80 J)
https://physics.nist.gov/cuu/pdf/sp811.pdf (reporting 1054.80 J)
|
ElementaryCharge
|
1.602176634×10^-19
|
1 electronvolt = 1.602176634×10-19 J
|
Exact definition (2019)
According to the 2019 revision of the SI base units.
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Notes:
•A calorie is a unit of energy originally defined as the amount of heat required to raise the temperature of one gram of water by one degree Celsius. The exact amount of heat needed depends on the atmospheric pressure and, most importantly, on the starting temperature of the water, because the heat capacity of water varies with temperature. As a result, several different definitions of the calorie have been used over time, each based on slightly different reference conditions. Due to this variation, the exact conversion between calories and joules has changed historically. In modern thermochemistry and nutrition, the accepted standard is the thermochemical calorie, which is defined to be exactly 4.184 J.
•A British Thermal Unit (BTU) was originally defined as the amount of heat required to raise the temperature of one avoirdupois pound of liquid water by one degree Fahrenheit at a pressure of one atmosphere. As with the calorie, the heat required depends slightly on the initial temperature of the water, which has led to several different BTU definitions. These definitions differ by up to about 0.5 percent. The variations arise from using different reference temperatures for water, such as 39 °F, 59 °F, the mean interval from 32 °F to 212 °F, or other standardized reference points. The most widely used definition today is the International Table BTU (BTU(IT)), which is based on the International Table calorie. Source: https://en.wikipedia.org/wiki/British_thermal_unit
POWER
Variable
|
Value
|
Meaning
|
Notes
|
OneHorsepowerMechanicalHPEquals_ftlbf_per_min
|
33000
|
1 Mechanical horsepower = 33,000 ft·lbf/min
|
Classical Watt definition
|
OneHorsepowerMetricPSEquals_kgfm_per_s
|
75
|
1 Metric horsepower = 75 kgf·m/s
|
DIN exact definition
|
OneHorsepowerElectricalEquals_Watt
|
746
|
1 Electrical horsepower = 746 W
|
Exact value used in electrical engineering
|
TEMPERATURE
Unit (symbol)
|
Definition
|
Celsius (°C)
|
-
|
Fahrenheit (°F)
|
[°F] = [°C] × 9/5 + 32
|
Kelvin (K)
|
[K] = [°C] + 273.15
|
Rankine (°R)
|
[°R] = ([°C] + 273.15) × 9/5
|
Delisle (°D)
|
[°De] = (100 - [°C]) × 3/2
|
Newton (°N)
|
[°N] = [°C] × 33/100
|
Réaumur (°Ré)
|
[°Ré] = [°C] × 4/5
|
Rømer (°Rø)
|
[°Rø] = [°C] × 21/40 + 7.5
|
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