A millimeter is a unit of length equal to one-thousandth of a meter. The **prefix** of 'Mille' is Latin for 'one thousandth'.

It is part of the metric system of measurement alongside things like meters, **grams**, **seconds**, and amperes.

The metric system is a base-ten system. That means you can convert between metric units by multiplying by 1000, 100, or 10, and so on.

This system is accepted internationally as a decimal system of measurement. It is part of a set of base units also known as the International System of Units (SI).

#### The Meter

The meter is defined as 1/299,792,458 of the distance that light covers in a second. A millimeter is one-thousandth of a meter.

By multiplying this distance-of-light figure by 1,000, we get the technical definition of a millimeter.

### Uses

The millimeter is used for small lengths. Or in situations calling for great detail in longer lengths, such as in industrial design.

A standard ruler measures 300mm. The millimeter is generally the smallest unit of measurement of a metric ruler.

### Compared To Inches

A millimeter is equal to approximately 0.039370 inches.