How this calculator works
Electricity is billed in kilowatt-hours (kWh): the power in kilowatts times the hours it runs. A 1,500 watt heater is 1.5 kW, so one hour uses 1.5 kWh. Multiply by your price per kWh to get the cost. Appliances that cycle (a thermostat heater, an air conditioner, a fridge) do not draw full power all the time, so the calculator lets you enter the average share of the rating.
Worked example: a 1,500 W space heater running at full power for 8 hours a day uses 12 kWh a day, which costs $2.04 a day at 17 cents. Over 30 days that is 360 kWh and $61.20, or $734 if it ran that way for twelve months. If its thermostat cycles it on half the time, the cost halves to about $30.60 a month.
Typical appliances at 17 cents per kWh
Typical running watts: check the label on yours. Appliances that cycle will average less.
| Appliance | Typical watts | Cost per hour | Per month at 4 h a day |
|---|---|---|---|
| LED light bulb (60 W equivalent) | 9 W | $0.00 | $0.18 |
| Ceiling fan | 50 W | $0.01 | $1.02 |
| Laptop | 50 W | $0.01 | $1.02 |
| 55-inch LED TV | 80 W | $0.01 | $1.63 |
| Desktop computer | 200 W | $0.03 | $4.08 |
| Dehumidifier (35 pint) | 450 W | $0.08 | $9.18 |
| Window air conditioner (8,000 BTU) | 700 W | $0.12 | $14.28 |
| Microwave oven | 1,100 W | $0.19 | $22.44 |
| Space heater (high) | 1,500 W | $0.26 | $30.60 |
| Hair dryer | 1,800 W | $0.31 | $36.72 |
| Electric clothes dryer | 5,000 W | $0.85 | $102.00 |
| Electric car charger (Level 2) | 7,200 W | $1.22 | $146.88 |
Tips before you buy
- The watts on a nameplate are the maximum. A fridge rated 150 W averages much less, because the compressor cycles. A plug-in watt meter tells you what an appliance really uses.
- The biggest costs in a home are heating and cooling, water heating, the dryer and an electric car, not lights and chargers. Look at those first.
- Standby power is small per device but adds up. 30 watts left on all year uses about 263 kWh, which is about $45 at 17 cents per kWh. A smart power strip turns devices off at the wall.
- If your utility charges more at peak hours, price the hours you actually run the appliance at that rate.
- Check the EnergyGuide label when buying: it shows the yearly kWh and cost. A higher purchase price for an efficient model often pays back over a few years.
Tools & materials for this project
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Frequently asked questions
How much does it cost to run a space heater?
A 1,500 W space heater at full power costs about 26 cents an hour at 17 cents per kWh, so about $2 for an 8-hour day, or $61 for a month of 8-hour days. Thermostat cycling lowers it.
How do I calculate the cost of electricity for an appliance?
Divide the watts by 1,000 to get kilowatts, multiply by the hours it runs to get kWh, and multiply by your price per kWh.
How many kWh does a 1,000 watt appliance use?
One kWh for every hour it runs at full power: 24 kWh in a day of continuous use.
How do I convert amps to watts?
Multiply the amps by the volts. A 15 A appliance on a 120 V outlet draws up to 1,800 W, and a 30 A load at 240 V is 7,200 W.
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