The basic unit for length in the metric system of measurement is the metre (m).

For measuring the lengths of short distances and objects, rulers can be used, using suitable units from the table below.

The commonly used units are millimetres, centimetres, metres and kilometres.

Unit
Symbol
Examples
millimetres
mm
Green peas are about 5 mm wide.
centimetres
cm
A pen is about 12 cm long.
metres
m
Most cars are about 3 to 5 metres long.
kilometres
km
Distance from London in England to Paris in France is 279 km.

Converting between Units

To convert between the units shown in bold in the first column and the units in the second column, multiply or divide by the factors indicated in the third column.

Unit
Convert to
Action
millimetres (mm)
cm
÷ 10
m
÷ 1000
km
÷ 1 000 000
centimetres (cm)
mm
× 10
m
÷ 100
km
÷ 100 000
metres (m)
mm
× 1000
cm
× 100
km
÷ 1000
kilometres (km)
mm
× 1 000 000
cm
× 100 000
m
× 1000

Examples

1. To change 8 cm into mm − multiply by 10.

8 cm = 8 × 10 mm = 80 mm

2. To change 500 m into km − divide by 1000

500 m = 500 ÷ 1000 km = 0.5 km