Lesson 2 of 9
Choosing the right unit
Show on a big screenAn ant, a table and a road need different units.
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Step 1 of 5
- Four units: mm, cm, m, km.
- An ant is tiny.
- A pencil fits in your hand.
- A table is room-sized.
- A road is city-sized.
- Millimetre (mm) — a unit for tiny things, like an ant.
- Centimetre (cm) — a unit for things you can hold, like a pencil.
- Metre (m) — a unit for a table or a door.
- Kilometre (km) — a unit for a road between cities.
10 mm = 1 cm. 100 cm = 1 m. 1000 m = 1 km.
Rule: Use the largest unit that still gives 1 or more.
Check km first. Then m, then cm, then mm.
Example: a pencil is 14 cm long. In m that is 14 ÷ 100 = 0.14 m. That is less than 1. So use cm.
Another: a table is 120 cm long. In m that is 120 ÷ 100 = 1.2 m. That is 1 or more. So use m.
Watch out!
A bigger number can be a shorter length. 90 mm is shorter than 1 m, which is 1000 mm.
Try the lab to finish this lesson.