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# Units of Length and Conversions

When we measure the length of an object, we use the most suitable unit of measurement depending on the size of the object. The smallest unit of length is millimetre (mm), followed by centimetre (cm), then metre (m) and finally a kilometre (km).

The SI (International System of units) uses metre as a standard for expressing length, so lengths can be expressed as a dimension of the metre.

‘Milli’ means one-thousandth, so 1 mm  = m

‘Centi’ means one- hundredth, so 1 cm  = m

Kilo means a thousand, so 1 km  =  1000 m

The table below gives the main units of length and their conversions.

 Table of Units 10 millimetres (mm) = 1 centimetre (cm) 100 centimetres (cm) = 1 metre (m) 1000 metres (m) = 1 kilometre (km)

In order to convert a larger unit to a smaller unit of length – multiply it by the conversion factor

And to convert a smaller unit to a larger unit of length – divide it by the conversion factor.

The pictorial diagram will highlight the conversions of the various units of length: ## Some examples of units of length and conversion of units are:

Example 1: 20 mm to cm.

Here we are converting from millimetre to centimetre (smaller to larger), so we divide by conversion factor (in this case 10).

So 20 mm  = =  2 cms

Example 2: 450 cm to metre

Here we are converting from centimetre to metre (again smaller to larger), so we divide by conversion factor (in this case 100).

So 450 cm  = =  4.5 m

Example 3: 3 cm to mm

Here we are converting from centimetre to millimetre (larger to smaller), so we multiply by conversion factor (in this case 10).

So 3 cm  =  3 x 10  =  20 mm

Example 4: 2.46 m to cm

Here we are converting from metre to centimetre (again larger to smaller), so we multiply by conversion factor (in this case 100).

So 2.46 m  =  2.46 x 100  =  246 cm

Example 5: 2026 m to kilometre

Here we are converting from metre to kilometre (smaller to larger), so we divide by conversion factor (in this case 1000).

So 2026 m  = =  2.026 km