Units and Conversion Factors

Units of Length

Metric System

  • meter (m) = 39.37 inches (in.) = 1.094 yards (yd)
  • centimeter (cm) = 0.01 m (exact, definition)
  • millimeter (mm) = 0.001 m (exact, definition)
  • kilometer (km) = 1000 m (exact, definition)

US System

  • angstrom (Å) = 10–8 cm (exact, definition) = 10–10 m (exact, definition)
  • inch (in.) = 2.54 cm (exact, definition)
  • yard (yd) = 0.9144 m
  • mile (US) = 1.60934 km

Units of Volume

Metric System

  • liter (L) = 0.001 m3 (exact, definition) = 1000 cm3 (exact, definition) = 1.057 (US) quarts
  • milliliter (mL) = 0.001 L (exact, definition) = 1 cm3 (exact, definition)
  • microliter
    (μL)(\mu\text{L})
    = 10–6 L (exact, definition) = 10–3 cm3 (exact, definition)

US System

  • liquid quart (US) = 32 (US) liquid ounces (exact, definition) = 0.25 (US) gallon (exact, definition) = 0.9463 L
  • dry quart = 1.1012 L
  • cubic foot (US) = 28.316 L

Units of Mass

Metric System

  • gram (g) = 0.001 kg (exact, definition)
  • milligram (mg) = 0.001 g (exact, definition)
  • kilogram (kg) = 1000 g (exact, definition) = 2.205 lb
  • ton (metric) =1000 kg (exact, definition) = 2204.62 lb

US System

  • ounce (oz) (avoirdupois) = 28.35 g
  • pound (lb) (avoirdupois) = 0.4535924 kg
  • ton (short) =2000 lb (exact, definition) = 907.185 kg
  • ton (long) = 2240 lb (exact, definition) = 1.016 metric ton

Units of Energy

  • 4.184 joule (J) = 1 thermochemical calorie (cal)
  • 1 thermochemical calorie (cal)
    =4.184×107erg=4.184\times {10}^{7}\text{erg}
  • erg = 10–7 J (exact, definition)
  • electron-volt (eV)
    =1.60218×1019J=23.061kcalmol1=1.60218\times {10}^{-19}\text{J}=23.061\text{kcal}{\text{mol}}^{-1}
  • liter∙atmosphere = 24.217 cal = 101.325 J (exact, definition)
  • nutritional calorie (Cal) = 1000 cal (exact, definition) = 4184 J
  • British thermal unit (BTU) = 1054.804 J[2]

Units of Pressure

  • torr = 1 mm Hg (exact, definition)
  • pascal (Pa) = N m–2 (exact, definition) = kg m–1 s–2 (exact, definition)
  • atmosphere (atm)  = 760 mm Hg (exact, definition) = 760 torr (exact, definition) = 101,325 N m–2 (exact, definition) = 101,325 Pa (exact, definition)
  • bar = 105 Pa (exact, definition) = 105 kg m–1 s–2 (exact, definition)



  1. BTU is the amount of energy needed to heat one pound of water by one degree Fahrenheit. Therefore, the exact relationship of BTU to joules and other energy units depends on the temperature at which BTU is measured. 59 °F (15 °C) is the most widely used reference temperature for BTU definition in the United States. At this temperature, the conversion factor is the one provided in this table.
  2. BTU is the amount of energy needed to heat one pound of water by one degree Fahrenheit. Therefore, the exact relationship of BTU to joules and other energy units depends on the temperature at which BTU is measured. 59 °F (15 °C) is the most widely used reference temperature for BTU definition in the United States. At this temperature, the conversion factor is the one provided in this table.

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