Friday, 22 Feb 2019

Calculating Your Electricity Consumption

energy calculations

Determining the electricity consumption for each appliance is one of the most effective approaches towards reducing the energy bills. As a consumer, the figures enable you to identify the equipment and processes that consume most of the energy on a daily or monthly basis.

Calculating the electricity that each appliance uses allows the consumers to find out the biggest energy hogs, hence providing them with the opportunity to adjust how they use the appliance or even consider upgrading to more efficient systems.

Costly energy losses

determine power rating or usageElectricity consumption depends on the rating of the appliance and the duration it remains in operation. While most of the energy should ideally perform useful work, some of these go to waste, either due to inefficiencies or incorrect use of the equipment. For example, if you leave a computer powered on when going to sleep, it will continue using the electricity unnecessarily.

Similarly, putting on lights when there is enough daylight or no one in the room means more energy use when the light output has no use. For this reason, even the low power equipment that is inefficient or incorrectly used may consume a lot of electricity. In fact, this can even exceed the electricity consumption by the high power equipment.

For example, leaving a 100 Watts electric bulb on for 10 hours will consume 1 kW of electricity. On the other hand, using a 1000W electric appliance such as kettle for 30 minutes will consume only 0.5 Kilowatt hour. It is therefore important to pay attention to every load in the household or organization since these can lead to unnecessary electricity consumption.

Typically, most of the older equipment consumes more energy compared to the newer models. The energy use varies according to the equipment function, size, and design. For instance, typical dryer uses between 1800 and 5000 watts, a laptop 50 watts, and a washer between 350 and 500 watts.

Calculating the electricity consumption for an appliance

Users can track their daily, monthly or annual energy consumption by just using simple calculations, provided that they know the power rating of the appliance and the number of hours it is used per day.

The power rating is usually expressed in watts, and multiplying this with the number of hours gives the usage in watts hours. However, the utility companies’ charges per Kilowatt hour and the watts must, therefore, be divided by 1000. I.e. Wattage rating X number of hours = Power consumption (Watts hour)

Consumption in Kilowatt hour = Power consumption Watts hour/1000 (kWh)

Determining power rating or usage

cost of electricity consumptionIt is easy to determine the electricity consumption of an appliance from its documentation, or the specifications sticker on the equipment. This provides the information such as the voltage, current, frequency, and power rating of the equipment. However, some equipment may not have this information while some may have worn out or invisible writing, hence, making it hard to see the rating.

In such a circumstance, consumers can use energy meters such as the Kill a Watt device. This plugs into the electrical outlet and has its own electrical outlet to connect the equipment and measure its energy use. A typical meter will have a digital readout to show the amount of electricity used over a given time.

Some models of the energy meters have the ability to determine and display other parameters besides the electricity consumption. These have additional capabilities to monitor the power quality, voltage levels, and the power factor and line frequency.

Once you get the energy rating, multiply the figure by the number of hours that the machine is in use per day, monthly or annually depending on what you are looking for. If you use the equipment on a daily basis and for the same number of hours per day, you can use this figure to determine the total usage per week or month by multiplying by 7 or 30/31 respectively.

Estimating the cost of electricity consumption

Once you calculate the number of kilowatts you consume per month, the next step is to calculate the amount it will cost to run the appliance for a month or any other period. Check your last electricity bill and see the rate you paid per kWh. Assuming it is something like 10 cents, multiply the total kilowatt hour with the figure to get the amount you pay per month or year for each of the appliances.

How to do energy calculations

calculating electricity consumptionYou can either do manual calculations or use offline or online electricity consumption calculators where you only need to select your equipment, rating, and the number of hours used per day. The tool will then give you the daily, monthly and annual totals. Tools with the cost field will calculate the amount you pay for the specified period.


A Wi-Fi router uses an average of 6 Watts per hour and would, therefore, use 96 watt hour per day or 2.8 Kilowatt hour per month when left on 24 hours a day. Assuming a rate of 10 cents per kilowatt, you will spend 2.8 x 0.1 = $ 0.28 per month on the router.

On the other hand, equipment such as the central air conditioner that consumes between 3000 and 5000 Watts per hour would cost more to run. A typical 3500W conditioner running for 9 hours during the hot days will consume about 31500 Watts per day or 31.5 kWh and will cost $3.15 to run every day and $94.5 per month.


With rising energy costs, most consumers would be glad to reduce the energy consumption. One way of achieving this is by finding out what the electrical equipment consumes when in operation.

Determining the electricity consumption by each appliance enables the users to adjust how they use them or consider upgrading the inefficient models.