How to find out how much energy you use

Perhaps the most obvious way of finding out just how much electrical energy is being used by an appliance is to turn everything else in your house off and take two meter readings exactly one minute or ten minutes apart. This will give you an approximate figure which you can then use to calculate its power demands over longer periods based on your own usage estimates.

You may not want to do this however, as apart from the inconvenience of it all, you probably do not want to be turning off your fridge or freezer unnecessarily.

A far easier method is to check out the power rating label on your appliance, usually near where the power cable goes in or on the body of an external transformer.

Although the label may only tell you how many amps a device uses in normal operation, this figure can be used to work out the power rating simply by multiplying it by the mains voltage.

If you are using a DC powered device that requires an external transformer, then you need to multiply the number of amps by the stated DC voltage, rather than the mains voltage, so if it says INPUT 10V, 2A for instance, then the power rating will be ten volts multiplied by two amps, which works out as being twenty watts.

Mains voltages can vary based on a number of factors including the standard of wiring in your house and the state of repair of the local sub station. Although the UK mains voltage is supposed to be 240v, this is really a maximum rating rather than an everyday reality. Appliances that are stated as being set up to work with a 240v supply can actually usually work with a range of voltages between 220 and 240 volts.

Even if you suspect that your mains voltage is somewhat less than the maximum of 240v, it is still a good idea to use this figure in any energy calculations that you are doing, as a voltage drop can be a temporary state of affairs.

You may see a switch on the back of your device to allow it to be run using mains voltages of between 100 and 240 volts. This is so that the device can be used in countries such as the US who have a different mains supply voltage to the UK. In the UK, you should always leave this switch set to 240v for safety reasons.

Make sure you get the right electricity supply with British Gas, the UK's cheapest electricity supplier on average.