The kilowatt-hour (kWh) is a unit of energy that is normally used as a billing unit for electricity supplied to consumers by electric distribution companies. As evident from the formula, a kWh is equal to 1,000 watts constantly transmitted over a period of one hour. For instance, an incandescent bulb or tungsten filament bulb rated 100 watts will consume 1 kWh if lit for 10 hours. Similarly a 1.5 ton air conditioner rated at 2,000 watts will consume 1 kWh every 30 minutes or 2 kWh in one hour. If the same air conditioner operates for 5 hours every day during a 30-day month, the total kWh consumed will be 300 for that month or billing cycle.
Although, it is unclear if 1 kWh translates to 1 billable unit of electricity in Pakistan on the electricity meters installed by distribution companies, it still serves as a good reference to measure household electricity consumption. Due to the recent changes in the electricity meters, negligence on part of distribution companies and tariff hikes; there is plenty of disparity in terms of electricity consumption and resulting electric bills. Additionally, tariffs during off-peak hours and peak hours vary which need to be factored in while calculating the electricity bill.
Going back to our example; if our 1.5 ton air conditioner operates for 5 hours each day for an entire month resulting in 300 kWh, the resulting electricity bill will be 300 x tariff (PKR 17 per unit/kWh) = PKR 5,100. This example uses a tariff multiplier of PKR 17 per unit. A breakdown of tariffs for off-peak and peak are listed on the monthly electricity bill from the respective electric supply company.
Most appliances have power consumption in watts listed on them and can be found on the rear side of the unit along with other specifications. Therefore, to calculate the estimated cost of operating a specific appliance, its power consumption needs to be converted to kilowatt-hours (kWh). An LCD TV that has a power rating of 200 watts or 0.2 kilowatts (KW) will consume 1 kWh in 5 hours (0.2 kWh in 1 hour) or 3.3 watts (200/60) per minute. Since electricity consumed by typical households are to the tune of hundreds and thousands of units during a calendar month, kWh is a convenient unit of billing for electric companies and consumers.
Here’s a reference table of different appliances along with their typical power consumption in watts.
|Appliance/Electric Components||Typical power consumption in watts|
|PC desktop computer||300 – 400 W|
|Laptop computer||40 – 60 W|
|Refrigerator||150 – 300 W (when comp. active)|
|Light bulb||25 – 100 W|
|Speaker(s)||10 – 300 W|
|Microwave||100 – 1000 W|
|Air conditioner||1000 – 2000 W|
|LCD TV||30 – 300 W|
|LCD monitor||30 – 45 W|