International System of Units (SI) Prefixes

The International System of Units (SI) prefixes are conveniently used to express fractions or multiples of any given unit, and are particularly useful when working with very large or very small numbers. For example, 100 kilometers (km) can be used instead of 100,000 meters (m). As another example, it is more convenient to state that the diameter of a typical mammalian cell is approximately 10 μm rather than 0.00001 m (or 10 × 10^-6 m). The table below provides a complete list of the accepted SI prefixes.