Electricity Cost Calculator

Electricity is priced per kilowatt-hour (kWh): 25 cents per kWh, for example. But what is a kilowatt-hour, and what does it mean for the vacuum cleaner or the space heater?

What is a kilowatt-hour?

A kilowatt-hour is a unit of energy: the amount a one-kilowatt device uses in one hour.

Imagine a device with a power of 1,000 watts, or 1 kilowatt. Switched on for one hour, it uses 1 h × 1 kW = 1 kWh. For two hours, 2 kWh. Left on for a whole day, 24 kWh. At 25 cents per kWh, the day costs 24 × $0.25 = $6.

A vacuum cleaner or a hair dryer is close to that 1,000 watts.

Another example: an old 60-watt light bulb uses 0.06 kilowatts. Left on all day, it uses 24 h × 0.06 kW = 1.44 kWh, which costs 36 cents at the same price. An 8-watt LED bulb giving the same light costs less than 5 cents a day.

How many kilowatt-hours do devices use?

Energy use depends on the device’s power (watts) and how long it runs (hours). Two rules of thumb for saving energy:

• A device that runs for long periods should be as efficient as possible.
• A device that draws a lot of power should run for as short a time as possible.

In other words, it may be easier to use the sauna or the space heater less often than to find one that uses half the power. And swapping light bulbs for LEDs is easier than sitting in the dark.

The power is usually printed on the device’s label or in its manual. For devices that switch on and off by themselves, like a fridge, the yearly consumption on the energy label is more accurate: 291 kWh a year is about 0.033 kW on average.