Your Electricity Bill is charged by the Kilowatt Hour (kWh) or Unit. 1 kWh equals 1 Kilowatt (kW) or 1,000 Watts (W) being used for an hour. On most equipment that you buy in shops today, their power consumption is marked in Watts or Kilowatts. If the equipment is only marked in Amps you will need to use use the formula P=IV where

P= Power (Watts)
I= Current (Amps)
V= Volts

a pretty good indication can be arrived at as to how much it costs to run them.

We will take an average electric shower of 8kW at 230v and 8.5kW at 240v. Sometimes there will be two indications of power consumption as the UK voltage is being dropped from 240v to 230v which I believe should happen by 2006.

As we know how many kW the shower uses, it is relatively simple to work out the cost to run it. On you Electricity Bill the cost per Unit or kWh is shown in Pence. We will take take an example of 8.59p/kWh or Unit.
We can therefore carry out the following calculation:

8kW (@230v) x 8.59p = 68.72p or if we divide the answer by 100 the answer will be £0.69. This means for every WHOLE hour the shower is being used it will cost roughly £0.69. This means for the average 10 min shower it will cost about £0.11.

8.5kW(@240v) x 8.59p = 73.015p or if we divide the answer by 100 the answer will be £0.73. This means for every WHOLE hour the shower is being used it will cost roughly £0.73. This means for the average 10 min shower it will cost about £0.12.

We will now look at your average 60W light bulb or lamp as an electrician refers to it. We must first convert Watts into Kilowatts which is done by dividing Watts by 1,000.

60W / 1,000 = 0.06 kW

By using the following calculation we can find out how much it costs to run the lamp for an hour assuming a voltage of 230v.

0.06kW x 8.59p = 0.5154p or if we divide the answer by 100 the answer will be £0.01. This means for every WHOLE hour the lamp is being used it will cost roughly £0.01.

If only the current is shown in Amps then it takes a longer to work out the cost. Using the formula P=IV, shown at the top of this page, we have to find out how many Watts the equipment uses. For an example we will assume that we are using something that draws 5 Amps and the voltage is 230 Volts.

P=IV
P= 5 (Amps) x 230 (Volts)
P = 1,150 Watts

We must now convert our answer into kW by dividing the answer of 1,150 Watts by 1,000 which gives you an answer of 1.15 kW. If we then multiply this new answer by 8.59p the answer is 9.8785p or £0.10. This means it will cost £0.10 to run the equipment constantly for a WHOLE hour.