Units and conversions

Metric units go up in tens, hundreds and thousands: 10 mm in a cm, 100 cm in a metre, 1000 m in a km, 1000 g in a kg, 1000 ml in a litre. To change to a smaller unit multiply; to a bigger unit divide.

Key facts

  • 1 cm = 10 mm; 1 m = 100 cm; 1 km = 1000 m.
  • 1 kg = 1000 g; 1 litre = 1000 ml.
  • Smaller unit: multiply. Bigger unit: divide.
  • Area units square the conversion: 1 m² = 10 000 cm².

Worked examples

Example 1

Change 3.4 km into metres.

  1. Metres are smaller, so multiply by 1000. 3.4 × 1000 = 3400 m

Answer: 3400 m

Example 2

A recipe needs 750 g of flour. How many kg is that?

  1. Kilograms are bigger, so divide by 1000. 750 ÷ 1000 = 0.75 kg

Answer: 0.75 kg

Example 3

How many cm² are in 3 m²?

  1. 1 m = 100 cm, so 1 m² = 100 × 100 cm². 10 000
  2. Three of them. 3 × 10 000 = 30 000 cm²

Answer: 30 000 cm²