Useful Conversion Factors

Units of Length

1 meter = 100 cm = 10-3 km = 1000 mm
1 light year = 9.4605 × 1015 meters
1 inch = 2.54 cm
1 mile = 1.609344 km
1 nanometer = 10-9 meters
1 Angstrom = 10-10 meters
1 Astronomical Unit (AU) = 1.496 x 1011 m
1 parsec = 3.26 light years

Units of Time

1 year = 365.244 days = 31,557,000 seconds

Units of Temperature

Let K be the temperature in kelvins, C in degrees Celsius, and F in degrees Fahrenheit. Then:

K = C + 273.15
F = 32 + 1.8 × C

Units of Mass

1 g = 10-3 kg = 1000 mg
1 lb = 453.59 g (only at the surface of the Earth . . . do you know why?)

Units of Energy

1 Joule = 0.2388 calories = 9.478 × 10-4 BTU = 107 ergs = 6.2415 x 1018 eV
1 Joule = 1 kg m2 / s2
1 erg = 1 g cm2 / s2

Units of Power

1 Watt = 1 J/s = 107 erg/sec = 1.341 × 10-3 horsepower

Units of Angle

1 radian = 57.2958 degrees


Commonly used metric system prefixes:

PrefixSymbolMeaningExample where often used
TeraT10121 TeV = 1012 eV
GigaG1091 Gyr = 1 billion years
MegaM1061 MHz = 106 Hz
kilok1031 km = 1000 meters
decid10-11 decibel = 1 dB = 0.1 bel
centic10-21 cm = 0.01 meters
millim10-31 mm = 0.001 meters
microµ10-61 µs = 10-6 seconds
nanon10-91 nm = 10-9 m
picop10-121 pF = 10-12 Farad
femtof10-151 fs = 10-15 seconds