kWh Calculator
Convert watts to kilowatt hours. Enter the power in watts and the run time in hours to calculate energy consumption in kWh — the same unit your utility uses on your electric bill. To see what that energy costs in dollars, use our energy cost calculator.
How to Calculate kWh
The formula to calculate kilowatt hours is: kWh = Watts × Hours ÷ 1,000. Multiply the power rating of the device (in watts) by the number of hours it runs, then divide by 1,000 to convert from watt-hours to kilowatt hours.
Formula: kWh = W × h ÷ 1,000
Monthly usage: kWh/month = daily kWh × 30
Example 1:A 1,500-watt space heater running for 4 hours uses 6 kWh (1,500 × 4 ÷ 1,000 = 6). At a typical electricity rate, that single evening of heating shows up directly on your bill.
Example 2:A 60-watt device left on for 24 hours uses 1.44 kWh (60 × 24 ÷ 1,000 = 1.44). Small loads add up when they run around the clock — this is why “always-on” devices matter for monthly usage.
Monthly usage: Once you know the daily kWh, multiply by 30 to estimate the monthly total. The space heater above at 4 hours per day would use about 180 kWh per month (6 × 30). To translate kWh into dollars on your bill, head to the energy cost calculator or the electricity bill calculator.
If your appliance lists amps instead of watts, first convert with Watts = Volts × Amps — or work backward from wattage using our watts to amps calculator.
Appliance kWh Usage Chart
Typical daily and monthly kWh usage for common household appliances (monthly = daily × 30):
| Appliance | Watts | Hours/Day | kWh/Day | kWh/Month |
|---|---|---|---|---|
| LED Light Bulb | 10 W | 5 h | 0.05 kWh | 1.5 kWh |
| Ceiling Fan | 75 W | 8 h | 0.6 kWh | 18 kWh |
| TV (LED, 50″) | 100 W | 4 h | 0.4 kWh | 12 kWh |
| Refrigerator (avg. draw) | 150 W | 24 h | 3.6 kWh | 108 kWh |
| Desktop Computer | 200 W | 8 h | 1.6 kWh | 48 kWh |
| Dishwasher | 1,200 W | 1 h | 1.2 kWh | 36 kWh |
| Window AC Unit | 1,200 W | 8 h | 9.6 kWh | 288 kWh |
| Space Heater | 1,500 W | 6 h | 9 kWh | 270 kWh |
| Clothes Dryer (Electric) | 3,000 W | 1 h | 3 kWh | 90 kWh |
| Water Heater (Electric) | 4,500 W | 3 h | 13.5 kWh | 405 kWh |
| EV Charging (Level 2) | 7,200 W | 2 h | 14.4 kWh | 432 kWh |
Wattages and run times are typical estimates — check your appliance nameplate for exact ratings. To estimate what each appliance costs to run, use the appliance cost calculator.
kWh vs kW: What's the Difference?
Kilowatts (kW) measure power — the rate of energy use. Kilowatt hours (kWh) measure energy — the total amount used over time. A kilowatt tells you how fast a device consumes electricity at any given moment; a kilowatt hour tells you how much it has consumed in total.
Think of it like driving a car: kW is your speed (miles per hour) and kWh is the distance you've traveled(miles). Driving 60 mph for 2 hours covers 120 miles — just as running a 2 kW appliance for 3 hours consumes 6 kWh. Your utility bills you for the distance (kWh), not the speed (kW).
kW (power): 1 kW = 1,000 watts. A snapshot of demand at one instant.
kWh (energy): 1 kWh = 1 kW sustained for 1 hour. What accumulates on your meter.
This is why a high-wattage appliance used briefly can consume less energy than a low-wattage one running constantly: a 3,000 W dryer used 1 hour per day (3 kWh) uses less than a 150 W refrigerator running 24 hours (3.6 kWh).
Reading Your Electric Meter
Your electric meter records cumulative kWh — it only counts up, like a car's odometer. To find how much energy you used in a period, subtract the earlier reading from the later one. If your meter read 45,210 kWh last month and reads 46,090 kWh today, you used 880 kWh.
Digital (smart) meters display the kWh total directly and report usage to your utility automatically — many utilities offer hourly usage data online. Analog dial metershave 4–5 dials that alternate direction; read each dial left to right, taking the lower number when the pointer sits between two digits.
Comparing your own meter readings against your bill is the simplest way to verify you're being billed correctly. To estimate your whole-home usage from the ground up, try the home energy cost calculator.
Frequently Asked Questions
How do I calculate kWh from watts?
Multiply the wattage by the hours of use, then divide by 1,000. The formula is: kWh = Watts × Hours ÷ 1,000. For example, a 1,500-watt space heater running for 4 hours uses 6 kWh (1500 × 4 ÷ 1000 = 6). To get monthly usage, multiply the daily kWh by 30.
What is a kilowatt hour?
A kilowatt hour (kWh) is a unit of energy equal to using 1,000 watts of power for one hour. It's the standard unit your electric utility uses to measure and bill your consumption. A 1,000-watt appliance running for 1 hour, or a 100-watt appliance running for 10 hours, both consume exactly 1 kWh.
How many kWh does the average home use per month?
The average U.S. home uses about 880 kWh per month, or roughly 29 kWh per day, according to the U.S. Energy Information Administration. Usage varies widely by region, home size, and heating type — homes with electric heat or central air conditioning can easily exceed 1,500 kWh in peak months, while small apartments may use under 500 kWh.
How many kWh does a 1500 watt heater use per hour?
A 1,500-watt heater uses 1.5 kWh for every hour it runs at full power (1500 ÷ 1000 = 1.5). Running it 8 hours a day would consume 12 kWh per day, or 360 kWh per month — often one of the largest single loads on a winter electric bill.
What is the difference between kW and kWh?
Kilowatts (kW) measure power — the rate at which energy is used at any instant. Kilowatt hours (kWh) measure energy — the total amount used over time. It's like the difference between speed and distance: kW is how fast you're using electricity, and kWh is how much you've used. A 2 kW appliance running for 3 hours consumes 6 kWh.
How do I calculate my monthly kWh usage for one appliance?
First calculate the daily usage: Watts × Hours per day ÷ 1,000 = kWh per day. Then multiply by 30 for the monthly total. For example, a 150-watt refrigerator compressor averaging 24 hours per day uses 3.6 kWh per day (150 × 24 ÷ 1000), which is about 108 kWh per month (3.6 × 30).
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