# Estimating measures

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Make cross-curricular links to numeracy with these measurement activities for ages 7-11

Estimates of measures are educated guesses based on comparisons with quantities that we already ‘know’. For example, we might estimate the width of a book using a mental image of a 30cm ruler, the length of a room using rounded multiples of our own height, or the volume of water in a fi sh tank using an image of a litre carton of fruit juice. In order to develop their estimation skills, children need to explore, develop and internalise a number of their own mental images or ‘yardsticks’. They also need lots of practice, so that they can develop their spatial skills and improve upon their accuracy and consistency.

### Talking points:

• What sort of mental images or techniques could you use when estimating counting seconds, for example ‘one Mississippi, two Mississippi…’?
• Does the degree of accuracy required for a ‘good’ estimate remain constant?
• What’s an acceptable range for an estimate of the width of this window or mass of this book or length of this pause?
• When would it be appropriate to estimate rather than measure?

Children should be encouraged to give a range (for example, 1.5-2kg) rather than a precise figure (for example, 2.4kg). They need to recognise that accurate estimation not only requires the measurement to fall within the range given in their estimate, but also involves setting a ‘suitable’ range that is as small as is appropriate. For example, a range of 2cm is appropriate for an estimation of the length of a pencil, but not for an estimation of the length of a car. Children will also need to think about the circumstances where measurement should be used in place of estimation.

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