kWh Calculator
Enter an appliance’s power in watts, how long it runs and your electricity rate to find energy use in kWh and the cost per day, month and year.
How to calculate kWh
kWh = watts × hours ÷ 1,000 Cost = kWh × rate per kWh
Worked example
A 1,500-watt space heater running 5 hours a day uses 1,500 × 5 ÷ 1,000 = 7.5 kWh a day, or 225 kWh over 30 days. At $0.16 per kWh that costs $36 a month.
Typical appliance wattage
| Appliance | Typical watts |
|---|---|
| LED bulb | 8–12 |
| Laptop | 30–70 |
| Refrigerator (running) | 100–250 |
| Microwave | 800–1,200 |
| Space heater | 1,500 |
| Clothes dryer | 2,000–5,000 |
Appliances that cycle on and off, like fridges and air conditioners, use less than their rated watts × hours. A plug-in energy meter gives the most accurate reading.
Frequently asked questions
What is a kWh?
A kilowatt-hour is the energy used by a 1,000-watt device running for one hour. It is the unit on your electric bill.
How do I find my electricity rate?
Divide your bill total by the kWh used, or check the rate per kWh printed on the bill.
How do I convert amps to watts?
Multiply amps by volts. A 10-amp device on a 120-volt circuit uses about 1,200 watts.
Does standby power count?
Yes. Many devices draw a few watts when switched off, which adds up over a year.
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