Kilo, centi, milli: the metric system made simple

Before the metric system, people measured with feet, inches, yards and miles, and every country had its own versions. New Zealand switched to the metric system in the late 1960s and 1970s. Now almost the whole world uses the same units, and they all work in tens, hundreds and thousands.

One base unit, many sizes

Each kind of measurement has a base unit: the metre for length, the gram for mass and the litre for capacity. A prefix in front tells you how big the unit is:

Converting

To change to a smaller unit, multiply: 2.4 m is 2.4 × 100 = 240 cm. To change to a bigger unit, divide: 850 mm is 850 ÷ 1000 = 0.85 m. A quick check: smaller units mean more of them, so the number should get bigger.

Benchmarks: measuring with your body

You carry measuring tools everywhere. Your pace (one normal step) is probably 50 to 70 cm. Your arm span is about the same as your height. A door is about 2 m tall, a netball court is about 30 m long, and a litre of water has a mass of 1 kg. Benchmarks help you estimate, and estimating helps you catch mistakes: if you calculate that a garden bed is 240 m long, your benchmark tells you something has gone wrong.

Accuracy matters

Builders say 'measure twice, cut once'. Always write the unit, measure from the zero on the tape (not the end of the case), keep the tape straight and tight, and measure twice. For a garden bed, the nearest centimetre is fine. For a cupboard door, you need the nearest millimetre.