How it’s worked out
Electricity is sold by the kilowatt-hour (kWh): 1,000 watts for one hour. So:
kWh = watts × hours ÷ 1,000 Cost = kWh × price per kWh
A 100 W television on for 5 hours a day uses 0.5 kWh a day; at 0.25 a kWh that is 0.13 a day and 45.63 a year (365 days).
Worked examples at 0.25 a kWh
| Appliance | kWh a day | A day | A year |
|---|---|---|---|
| A 10 W LED bulb, 5 hours a day | 0.05 | 0.01 | 4.56 |
| A 100 W television, 4 hours a day | 0.4 | 0.10 | 36.50 |
| A 2,000 W heater, 3 hours a day | 6 | 1.50 | 547.50 |
| A 3,000 W kettle, 10 minutes a day | 0.5 | 0.13 | 45.63 |
A kettle draws a lot of power but for minutes at a time, so it costs less than an hour of a heater. Your own price per kWh is on your bill.
How to read the result
- The yearly cost is the headline: it’s the figure to compare appliances by.
- Hour and day costs under a penny are shown as “under 0.01”.
- A month is a twelfth of the year.
Common mistakes
- Using the label’s watts for something that cycles on and off, such as a fridge, freezer or heat pump: use the yearly kWh on its energy label instead.
- Typing the price in pence when the currency is pounds: 25p is 0.25.
- Leaving out the standing charge: it’s a daily fee you pay whatever you use, so it isn’t in an appliance’s cost.
How to use it
- Type the power from the label or plug, in watts.
- Type the hours a day it’s on and the days a week.
- Type your price per kWh from your bill.
Questions
How do I work out the cost of running an appliance?
Multiply its watts by the hours it’s on and divide by 1,000 to get kWh, then multiply by your price per kWh. A 100 W TV for 5 hours at 0.25 a kWh costs 0.13 a day.
How much does it cost to run a 2,000 W heater?
At 0.25 a kWh, 0.50 an hour, because it uses 2 kWh each hour it’s on at full power.
Is the standing charge included?
No. The standing charge is a fixed daily fee on many bills, paid however much you use, so it isn’t part of what one appliance costs.
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