The power or a device is measured in watts (W). A kilowatt means 1000 watts.

Energy is normally measured in joules (J) but when **calculating the cost of using electricity** energy is measure in kilowatt-hours (kWh).

Energy transfered = power x time

(kilowatt-hours, kWh) (kilowatts, kW) (hours, h)

Total cost

total cost = number of kilowatt-hours x cost of one kilowatt-hour

Example; If a 3 kW heater is used for 2 hours what was the total cost if every kW h of electricity costs 7 pence ?