Running 500 watts for one hour uses 0.5 kWh and costs $0.09 at the U.S. average of 18.19¢/kWh.
At 18.19¢/kWh — U.S. average, Jan–Aug 2026 (EIA).
| Period | kWh | Cost |
|---|---|---|
| Per hour of use | 0.5 | $0.09 |
| Per day | 0.5 | $0.09 |
| Per month | 15.2 | $2.77 |
| Per year | 183 | $33.20 |
| Where | ¢/kWh | Month | Year |
|---|---|---|---|
| U.S. | 18.19 | $2.77 | $33.20 |
| North Dakota (cheapest) | 12.46 | $1.90 | $22.74 |
| Hawaii (most expensive) | 46.41 | $7.06 | $84.71 |
| Hours a day | kWh a day | Per day | Per month | Per year |
|---|---|---|---|---|
| 1 h | 0.5 | $0.09 | $2.77 | $33.20 |
| 4 h | 2 | $0.36 | $11.07 | $133 |
| 8 h | 4 | $0.73 | $22.13 | $266 |
| 12 h | 6 | $1.09 | $33.20 | $398 |
| 24 h | 12 | $2.18 | $66.40 | $797 |
kWh is what you pay for: power (kW) times hours. 500 W is 0.5 kW, so every hour at full power is 0.5 kWh. The U.S. average residential price for Jan–Aug 2026 is 18.19¢ per kWh (EIA), which already spreads delivery and fixed charges over every kWh.
Appliances with a thermostat or compressor only draw full power part of the time; use the duty-cycle field in the calculator for those.
The full method, material data and tips are on the main electricity cost calculator page.