# Definition:Metric System/Length

## Definition

Various metric units of length which have specific names are as follows:

### Micrometre

The micrometre is a metric unit of length.

 $\displaystyle$  $\displaystyle 1$ micrometre $\displaystyle$ $=$ $\displaystyle 10^{-3}$ millimetre $\displaystyle$ $=$ $\displaystyle 10^{-6}$ metres

### Millimetre

The millimetre is a metric unit of length.

 $\displaystyle$  $\displaystyle 1$ millimetre $\displaystyle$ $=$ $\displaystyle 1000$ micrometres $\displaystyle$ $=$ $\displaystyle 10^{-3}$ metres

### Centimetre

The centimetre is the CGS base unit of length.

 $\displaystyle$  $\displaystyle 1$ centimetre $\displaystyle$ $=$ $\displaystyle 10$ millimetres $\displaystyle$ $=$ $\displaystyle 10 \, 000$ microns $\displaystyle$ $=$ $\displaystyle 0 \cdotp 01$ metres

### Metre

The metre is the SI base unit of length.

It is defined as the distance travelled by light in vacuum in $\dfrac 1 {299 \ 792 \ 458}$ of a second.

 $\displaystyle$  $\displaystyle 1$ metre $\displaystyle$ $=$ $\displaystyle 100$ centimetres $\displaystyle$ $=$ $\displaystyle 1000$ millimetres $\displaystyle$ $=$ $\displaystyle 10 \, 000$ microns

### Kilometre

The kilometre is a metric unit of length.

 $\displaystyle$  $\displaystyle 1$ kilometre $\displaystyle$ $=$ $\displaystyle 1000$ metres $\displaystyle$ $=$ $\displaystyle 100 \, 000$ centimetres $\displaystyle$ $=$ $\displaystyle 10^6$ millimetres