Decimals and measuring

Ages 9 to 12 Read alone or together · about 30 minutes

Read together

A decimal is a way of writing parts of a whole using place value. The point separates whole numbers from parts.

In 2.5, the 5 means five tenths. A tenth is one of ten equal parts: 0.1.

The metric system uses tens: 10 millimetres make 1 centimetre, and 100 centimetres make 1 metre.

Do it

1. Use a ruler. Measure a pencil in centimetres and millimetres: for example 17.4 cm.
2. Draw a number line from 0 to 1 divided into ten parts. Mark 0.3, 0.5 and 0.8.
3. Measure five objects at home. Write each length as a decimal in centimetres and then in metres.
4. Compare 0.4 and 0.35. Which is greater? Use a number line to check.

Talk about it

• How many tenths are in 1?
• Why is the metric system easy to convert?

For the grown-up

Decimals extend place value to the right of the point. Some countries write a comma instead of a point. Most of the world uses the metric system. The US also uses inches, feet and pounds, so you might practise both.

Mark as done

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Where this comes from

• Bureau International des Poids et Mesures (BIPM), The International System of Units (SI Brochure), on the metre and metric prefixes
• National Institute of Standards and Technology (NIST), Guide for the Use of the International System of Units (NIST Special Publication 811)

Written with AI assistance and checked against the sources listed. Please read it before sharing it with a child.