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Grade 5

Units of length (and conversions)


Which unit?

If we are comparing two lengths, but they are written in different units, all we need to do is change one of them. You may change from millimetres (m) to centimetres (cm), or you may go the other way. In fact, all we need to do is remember how to convert units, and we can do this with other measurements as well, such as metres (m) and kilometres (km)

Millimetres to centimetres

In this video, we will see how to remember whether to multiply or divide, to convert from mm to cm, and back again.

We can still use the same method if our number has decimals! Here are some examples, including decimals.


Worked Examples

Question 1

Convert $6.52$6.52 centimetres to millimetres. Write your answer as a decimal.

Question 2

Convert $25.97$25.97 millimetres to centimetres. Write your answer as a decimal.

  1. $25.97$25.97 mm = $\editable{}$ cm


What about metres and kilometres?

As long as we know how our units compare, we can convert these as well. Here's a quick refresher.


Worked example

Question 3

A skyscraper is $961$961 metres tall.

  1. What is the height of the building in kilometres? Give your answer in decimal form.

  2. What is the height of the building in centimetres?



We can use the following conversion chart to convert between units of measurement.

Standard conversions



Select and justify the most appropriate standard unit (i.e., millimetre, centimetre, decimetre, metre, kilometre) to measure length, height, width, and distance, and to measure the perimeter of various polygons


Solve problems requiring conversion from metres to centimetres and from kilometres to metres

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