How to Calculate Electricity Usage Cost and Charges

Ever since I needed to pay my own electricity bill because I no longer stay with my parents, it is important that I know how to calculate the electricity usage and charges for every electronic devices and electrical appliances. This knowledge will allow me to conserve energy and save money at the same time by not simply wasting the energy in the first place.

Most of the time when we purchase electrical appliances such as a television, you will find the power consumption being mentioned in the technical specifications. One example is the Panasonic 50″ Smart VIERA Plasma TV that stated 142W for “On mode Average Power Consumption”.

(W) stands of Watt and this piece of information is very important to calculate the usage charges. This is the information that you need to calculate the usage of the electrical appliances that you use in hours. Some doesn’t display Watt, but only Volt (V) and Ampere (A). To get Watt, simply multiple volt with ampere. For example V x A = W. Once you know the Watt, next thing you need to know is the current tariff rates offered by your electric utility company.

The current tariff and pricing rates in Malaysia by Tenaga Nasional Berhad (TNB) for residential consumer are as shown at the image below. You can also access the official TNB tariff webpage here.

The rates clearly shows that the more electricity your home uses, the more expensive it gets. Since the tariff are given in kWh (kilowatt hour), here is the formula to convert the Watt and Hour into kWh.

W x Hours / 1000 = kWh

Once we have the kWh, all we need to do now is to multiple with the rates given by Tenaga Nasional Berhad. Let us try calculating a few electrical appliances and see how much it cost to use them.

If you use a Philips 9W LED light bulb for 10 hours daily. How much would it cost per month?

First we need to get the kWh:
9W x 10Hours / 1000 = 0.09 kWh

Once we have the kWh, we are able to calculate how much it cost to use per day.
0.09kWh x 21.8(rate) = 1.962sen per day

For a whole month, just multiply 1.962 with 30 because a month consists of 30 days.
1.962sen x 30days = 58.86sen

We can clearly see that the Philips 9W LED light bulb is truly an energy saver because it only cost 58.86 cents per month if we use it 10 hours a day. The calculation formula is the same throughout the whole world, except for the rates offered by your country’s electric provider.

Let’s try another calculation that consumes more power. You boil water everyday for one hour using Burco’s 4 liter fast boiling with high power heater (2.4kW) kettle. How much is the charges for the whole month?

2.4kW x 1hour = 2.4kWh
2.4kWh x 21.8sen = 52.32sen
For the whole month, 52.32sen x 30 = 1569.6sen which equivalents to RM15.696

Since this is a fast boiling kettle with high power heater, it probably takes only 10 minutes to boil the water instead of an hour. Simply divide 53.32sen with 6, and it cost nearly 9 cents (8.72sen to be exact) to boil a water with this kettle.

If you need to know the electricity usage accurately, you will need to use an energy use monitor device such as the Belkin Conserve Insight. Just plugin the device to a power socket and then plug in the appliance that you want to monitor in the Belkin Conserve Insight outlet.

There is an online electricity bill calculator available in Tenaga Nasional Berhad’s website where you only need to select the category type and enter the total consumption in kWh to get your estimated bill. By comparing the electric usage from your previous electric bill and the current usage displayed on the meter to get the total kWh usage, you are able to get an instant estimation of your new electricity bill.