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Numbers, units and arithmetic
Numbers, units and arithmetic

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2.2 Converting units

A great advantage of the metric system of units is that conversion between units within the system is particularly easy. For example, ‘£1 is worth 100p’ is converting one pound into pence. To convert pounds to pence, you multiply by 100. So £2 is 200p, and £2.63 is 263p. (Remember that to multiply by 100, you move the digits two places to the left in the place value table.)

To convert from pence to pounds, you need to reverse this process, i.e. to divide by 100 (moving the digits two places to the right) so that 845p becomes £8.45. In the same way, any of the metric units can be converted simply by multiplying or dividing by ten, a hundred or a thousand. For example, the statement ‘1 m = 1000 mm’ tells you that to convert from metres to millimetres you multiply by 1000.

The general rule when converting units is: to convert from a larger unit (e.g. metres) to a smaller one (e.g. millimetres), multiply; to convert from a smaller unit to a larger one, divide.

Example 8

The measurements of the kitchen units in the example above were given in millimetres – a unit was 575 mm deep. What is this in metres?


To convert millimetres to metres, divide by 1000. So to convert 575 mm to metres, move the digits three places to the right:

  575.0 ÷ 1000 = 0.575.

So the answer is 0.575 m.

There is no handy metric system for time. There are 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day and 7 days in a week; a month may be 28, 29, 30 or 31 days long and a year may contain 365 or 366 days.