Length unit converter

The calculator converts length between millimetres, centimetres, decimetres, metres and kilometres. Choose the unit of the length you enter and the unit of the result next to the boxes. For example, a walk around a lake that is 2.5 km long is 2,500 metres.

How it works

Units of length go up in tens: each is ten times bigger than the one before. Only between the metre and the kilometre is the jump a thousand, because hectometres and decametres are hardly ever used.

When converting to a smaller unit, multiply; when converting to a larger unit, divide. A few typical conversions:

• 2.5 km = 2,500 m (multiply by 1,000),
• 175 cm = 1.75 m (divide by 100),
• 45 mm = 4.5 cm (divide by 10),
• 0.8 m = 80 cm (multiply by 100).

Things to watch out for

The most common mistake is moving the decimal point by the wrong number of places, usually between centimetres and metres. A quick check is common sense: an adult is about 1.75 m tall, that is 175 cm, not 17.5 cm. If you are working out the perimeter of a rectangle or the perimeter of a square, convert all the sides to the same unit before adding them.

If you are converting area or volume, the rule is not tens but hundreds and thousands. For those, see the area unit converter and the volume unit converter.