kWh Calculator
Your estimate
- Energy per month
- 180 kWh
- Energy per year
- 2,160 kWh
- Cost per month
- $32.40
- Cost per year
- $389
Kilowatt-hours used by any appliance — and what they cost.
Updated 2026-10-20 · Based on: Ohm’s law, NEC Chapter 9 Table 8, 210.20 and 310.16; DIN VDE 0100-520 for metric.
How to use the kWh Calculator
- Enter the power in watts.
- Enter the hours of use per day and the days per month.
- Read the kWh per day, month and year; open “More options” to set your rate per kWh.
Formula
kWh = watts × hours ÷ 1,000. 1 kWh is 1,000 W for one hour, or 100 W for ten hours.
kWh per month = kWh per day × days used; per year = × 12.
Worked example
With the values preset in the calculator above:
- Power
- 1,500 W
- Hours per day
- 4 hours per day
- Days per month
- 30 days per month
- Number of devices
- 1
- Energy per day
- 6 kWh
- Energy per month
- 180 kWh
- Energy per year
- 2,160 kWh
- Cost per month
- $32.40
- Cost per year
- $389
Watts to kWh examples
- 1,500 W for 4 h = 6 kWh a day, 180 kWh a month.
- 100 W for 24 h = 2.4 kWh a day.
- 60 W for 5 h = 0.3 kWh a day.
- 3,500 W (Level 1–2 EV charging) for 3 h = 10.5 kWh a day.
How many kWh does a house use?
The average US home uses about 850–900 kWh a month (around 10,500 kWh a year); homes with electric heat or an EV use far more. Your bill shows your monthly kWh — use it in the solar panel calculator to size a system.
kWh by wattage (4 hours a day)
| Power | Energy per day | Energy per month |
|---|---|---|
| 10 | 0.04 kWh | 1.2 kWh |
| 60 | 0.24 kWh | 7.2 kWh |
| 100 | 0.4 kWh | 12 kWh |
| 150 | 0.6 kWh | 18 kWh |
| 500 | 2 kWh | 60 kWh |
| 1,000 | 4 kWh | 120 kWh |
| 1,500 | 6 kWh | 180 kWh |
Frequently asked questions
How do I convert watts to kWh?
Multiply watts by hours and divide by 1,000: 2,000 W × 3 h = 6 kWh.
How many kWh does a fridge use?
A modern fridge uses about 1–2 kWh a day (30–60 kWh a month). Its label wattage is higher because the compressor cycles on and off.
What is the difference between kW and kWh?
kW is power (how fast energy is used); kWh is energy (power × time). A 2 kW heater running 3 hours uses 6 kWh.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.