Electrical energy is measured in kWh units (kilo-watt hours) which is equivalent to 1000W being used for one hour.

Most appliances have the power rating printed on the name plate.

Example: A hairdryer may have a rating of 1 200W. This appliance would use: 1 200 W each hour or 1.2 kWh units per hour.

If the hairdryer is used for only 10 minutes, it would use:
                        (1.2 kWh) x (10min/60min) = 0.2 kWh.

On the residential tariff Scale 4 Tariff this would cost (0.2 kWh) x (45.6430 cents/kWh) = 9.13 cents