Electricity cost calculator
Watts and hours in, kWh and cost per day, month and year out.
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Example
Example: what a 1,500 W space heater costs at 4 hours a day
A portable heater rated 1,500 W runs about 4 hours every evening, and the bill says 17 cents a kWh, taxes included. Type 1500 as the power and 4 as the hours a day, leave Every day, and type 0.17 as the price.
- An hour of use: 1,500 W ÷ 1,000 = 1.5 kWh, which costs $0.26 at $0.17.
- A day: 1.5 kWh × 4 h = 6 kWh = $1.02.
- A year: 6 kWh × 365 = 2,190 kWh = $372.30; a month is a twelfth of that, 182.5 kWh = $31.03.
| Appliance | Use | kWh a year | Cost a year at $0.17 |
|---|---|---|---|
| Space heater, 1,500 W | 4 h a day | 2,190 | $372.30 |
| Air conditioner, 800 W | 8 h a day | 2,336 | $397.12 |
| Tumble dryer, 2,500 W | 1 h, 3 days a week | 391.1 | $66.48 |
| Desktop computer, 200 W, 3 W standby | 4 h a day | 313.9 | $53.36 |
| Fridge, 35 W on average | 24 h a day | 306.6 | $52.12 |
| TV, 100 W | 5 h a day | 182.5 | $31.03 |
| 10 LED bulbs, 9 W each | 5 h a day | 164.3 | $27.92 |
| Games console, 150 W | 3 h a day | 164.3 | $27.92 |
The heater costs $1.02 a day and about $31 a month, $372.30 if it ran every evening of the year. Set fewer days a week, or a lower price per kWh, and every figure follows.
How it works
- Type the power in watts from the appliance’s label, or pick a common appliance for typical values.
- Type how many hours a day it runs and on how many days a week; add a standby draw if it stays plugged in.
- Type your price per kWh from your bill to see the cost per hour, day, month and year.
Frequently asked questions
- How do I calculate electricity cost?
- Watts × hours ÷ 1,000 gives kWh; kWh × your price gives the cost. A 100 W TV on for 5 hours uses 0.5 kWh a day; at $0.17 a kWh that is 8.5 cents a day, about $31 a year.
- Where do I find the watts?
- On the rating plate or in the manual (sometimes as amps: watts = volts × amps). Many appliances use less than the plate says most of the time, so a plug-in energy meter gives the truest figure.
- Why is the fridge only 35 W?
- A fridge’s compressor runs on and off all day. 35 W around the clock is about 300 kWh a year, typical of a modern fridge; the energy label gives your model’s kWh a year.
- What price per kWh should I use?
- The energy charge on your bill, including taxes. It does not include the fixed daily or monthly charge, which you pay whatever you use.
- How much does it cost to run a space heater?
- Watts × hours ÷ 1,000 × your price. A 1,500 W heater on for 4 hours uses 6 kWh: $1.02 a day at $0.17 a kWh, about $31 a month. Eight hours a day doubles it. A heater whose thermostat switches it off now and then uses somewhat less than its rating.
- How is standby counted?
- As watts for the hours the appliance is not in use. A 200 W computer used 4 hours a day with 3 W of standby draws 0.8 kWh in use plus 3 W for the other 20 hours: 0.86 kWh a day, 313.9 kWh a year, $53.36 at $0.17.
- Is anything uploaded?
- No. It is worked out in your browser, and nothing you type leaves your computer.