Orders of Magnitude

• 1 km = 1 kilometre = [103 m] = 1 000m

  1 cm = 1 centimetre = [10-2 m] = 0.01 m

  1 mm = 1 millimetre = [10-3 m] = 0.001 m

  1 µm = 1 micrometre = [10-6 m] = 0.000001m

  1 nm = 1 nanometre = [10-9 m] = 0.000000001 m

  The prefixes (e.g. "kilo-" or "centi-") above show the magnitude (size) of a value (or number). They can be put before different types of units. Here, we are using the unit for distance (metres, m).
• Prefixes before units show the magnitude of a number. For example, in kilometre, the prefix is kilo, and means 1,000. If something was 100 kilometres away, this is the same as writing 100,000 metres.