Scientific notation is a useful means to write out very large or very small numbers using powers of ten. Spelling out scientific notation numbers can be a mouthful. The number 5 x 10^{6} could be said “five times ten to the six”, but it is easier to say “five million”. We have words that express the very large and the very small.

The same is true for the metric system or SI units. These measurements are based on powers of ten, just like scientific notation. Every three powers of ten has its own metric prefix. There are a couple of special powers of ten that have their own prefix outside the ‘every three’ pattern.

The wavelength of microwaves are on the order of 10^{-6} meters. The prefix for 10^{-6} is micro, so you can say the wavelength of a microwave is on the order of one micrometer. (This also makes it obvious why they’re called microwaves.) The symbol for micro is the Greek letter μ. 1 micrometer is written as 1 μm.

The distance between the Earth and the Moon is about 384,000,000 meters. The Mega prefix (symbol M) means one million, so you could say the distance is 384 Megameters or 384 Mm.

Substituting the metric prefix can make doing calculations easier in your head. Use the prefix that applies to your situation. This table of metric prefixes has the standard names for each prefix used in science and measurements. It also shows the symbol used to represent these prefixes, their ‘power of ten’ and the number you are actually replacing with the prefix.