Idea 7of 22Builds onCould that really be its size?
Estimate first, then measure
Why guess a length before you measure it?
Today you'll discover
- how to estimate with a hand span
- how to measure with a ruler
- what a close estimate tells you
Think firstA hand span is about 20 cm
The book is a bit longer than one hand span. What is a good estimate?
Decide first, then press Next. Use the bracket over the book.
A book above a 30 cm ruler, with a blue bracket over it labelled a hand span, about 20 cm. A dashed mark shows the estimate, about 25 cm. Then the book is lined up with 0 and its far end reads 24 cm: estimate about 25 cm, measured 24 cm, close. The last step shows an eraser with five fingernail brackets over it.
See the whole ideathe big idea and the key word, in one place
The big idea
Estimate first with a benchmark, then measure. If the two are far apart, measure again.
Easy to get wrongIf you estimate about 25 cm and measure 250 cm, something is wrong: check where the ruler starts, and the unit.
Estimating with your handSpread your hand: about 20 cm. A desk two spans wide is about 40 cm.
Key word
- estimate
- a careful guess of a size, made with a benchmark before measuring
Ready to use it?
- Estimate a length, then measure it.
- Decide if a measurement is close to the estimate.