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Measurement: Length, Mass & Capacity

≈ 18 min
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We measure different things with different units, and pick the unit to suit the size of the job:

  • Length: millimetres (mm), centimetres (cm), metres (m), kilometres (km).
  • Mass (how heavy): grams (g), kilograms (kg).
  • Capacity (how much liquid fits): millilitres (ml), litres (l).

The units in each family are linked by tens, hundreds and thousands:

1 cm=10 mm1 m=100 cm1 km=1000 m1\,\text{cm} = 10\,\text{mm} \qquad 1\,\text{m} = 100\,\text{cm} \qquad 1\,\text{km} = 1000\,\text{m}
1 kg=1000 g1 l=1000 ml1\,\text{kg} = 1000\,\text{g} \qquad 1\,\text{l} = 1000\,\text{ml}

Worked example. How many centimetres are in 33 metres?

Since 1 m=100 cm1\,\text{m} = 100\,\text{cm}, three metres is 3×100=300 cm3 \times 100 = 300\,\text{cm}.

Which unit is best for measuring the length of a classroom?

How many centimetres are there in 33 metres?

A bag holds 2 kg2\,\text{kg} of rice. How many grams is that?

A large bottle of cool drink most likely holds about…