kWh Calculator
Convert watts and hours into kilowatt-hours per day and month, and see the cost at your electricity rate.
What your result means
A kilowatt-hour is one kilowatt of power used for one hour, and it's the unit your utility bills. This turns watts and run time into kWh per day and month, then applies your rate for cost. Knowing your monthly kWh is also the starting point for sizing solar — feed it into our PV calculator. For per-appliance running cost, see the electricity cost calculator.
How to use this calculator
- Enter the device wattage.
- Enter the hours it runs per day.
- Add your electricity rate for the cost figure.
- Read kWh per day and per month, plus the monthly cost.
- Use the monthly kWh to size a solar system if you're considering one.
The formula
Watts times hours is watt-hours; divide by 1,000 for kilowatt-hours. Multiply the daily figure by 30 for a monthly total, and by your rate for cost.
Worked example
A 1,000 W device running 5 hours a day uses 5 kWh daily and about 150 kWh a month. At $0.17 per kWh that's roughly $25.50 a month for that one device.
Energy use examples
| Device | Watts × hours/day | kWh/month |
|---|---|---|
| Laptop | 60 W × 6 | 10.8 kWh |
| TV (large) | 120 W × 5 | 18 kWh |
| Dishwasher | 1,800 W × 1 | 54 kWh |
| Pool pump | 1,100 W × 8 | 264 kWh |
| Central AC | 3,500 W × 6 | 630 kWh |
Tips & gotchas
- Your whole-home monthly kWh is on your utility bill — compare it to the sum of your devices.
- kWh, not watts, is what you pay for — a low-watt device left on all day can still add up.
- Use your annual average kWh when sizing solar, not a single peak month.
- Time-of-use rates make when you run things matter as much as how much.
- Pair this with the electricity cost calculator to see dollars per appliance.
Frequently asked questions
How do I calculate kWh?
Multiply watts by hours, then divide by 1,000. A 1,000 W device for 5 hours is 5 kWh. Multiply by days for a monthly total.
What is a kilowatt-hour?
One kilowatt of power used for one hour. It's the standard billing unit for electricity, so your rate is quoted per kWh.
How many kWh does a house use?
A typical US home uses about 850 to 950 kWh a month, though it varies widely with size, climate, and appliances.
How does kWh relate to solar?
Solar systems are sized to your kWh usage. Find your monthly kWh, then use the PV calculator to estimate the system size and panel count.
What's the difference from the electricity cost calculator?
This one leads with energy in kWh; the electricity cost calculator leads with dollars per day, month, and year. Same underlying math.
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