Units of mass
The unit of mass in the International System of Units is the kilogram, which is represented by the symbol 'kg'. Fractions and multiples of this basic unit include the gram (one thousandth of a kg, symbol 'g') and the tonne (one thousand kg), amongst many others.
In some fields or applications, it is convenient to use different units to simplify the discussions or writings. For instance,
- Atomic physicists deal with the tiny masses of individual atoms and measure them in atomic mass units.
- Jewelers normally work with small jewels and precious stones where masses are traditionally measured in carats, which correspond to 200 mg or 0.2 g.
- The masses of stars are very large and are sometimes expressed in units of Solar masses.
Traditional units are still in encountered in some countries: Imperial units such as the ounce or the pound were in widespread use within the British Empire. Some of them are still popular in the United States, which also uses units like the short ton (2,000 pounds, 907 kg) and the long ton (2,240 pounds), not to be confused with the metric tonne (1,000 kg).