You may come across a situation, whether for a particular device or for a scientific purpose, where you need to not only convert a kilojoule figure from a kilowatt-hour (kWh), but also determine the cost. The kilojoule is a small unit of energy in relation to the kWh. The kWh is the unit employed to determine home billing of electricity in general. It's the unit on your electric meter. To deduce the cost of a kilojoule, start with the cost per kilowatt hour, reflected on a recent power invoice or bill, and make the conversion.

Find the total cost on a recent invoice or bill from your power company. Use the total cost, not the stated cost per kWh unit, to get the real price you pay for every unit of power.

Divide the amount by kWh used. For example, if the total is £132.9, and you used 660 kWh during the bill period, the true cost per kWh is 31 cents.

Divide you result by 3,600. Here, the figure is .00861 cents.

Multiply the cost per kilojoule by kilojoules consumed to get a cost for use. For instance, if you have 53,000 kilojoules of use, the cost is £296.6