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We can draw straight lines using a ruler.

To position a ruler accurately, place the point that says 0 at the start of the line you are measuring.

With the ruler placed carefully on the line, measure the centimetres first, then the millimetres. These are represented with the small lines.

Here is a ruler and some straight lines for us to measure.

There are 10mm in 1cm. 1cm = 10mm.

We can round measures up if they are less than a whole cm.

If a number is 5mm or or above, we round it up to the nearest whole cm. So you could say 10cm 5mm is approximately 11cm.

If a number is less than 5mm, we round it down. So you could say 10cm 4mm is approximately 10cm.

We can draw shapes accurately by measuring them too. For example, we can draw a triangle and measure the sides, so that it is accurate.

Test your measuring skills with this quiz.