Electricity cost calculator
Enter a device's watts and how long it runs, or the yearly kWh from its EnergyGuide label. Then enter your electricity rate. You'll see the cost per day, month and year, and what a full recharge of a power station costs.
Cost to recharge a power station
The formula
Cost = kWh × price per kWh
Your utility bills you per kilowatt-hour (kWh), which is 1,000 watt-hours. A 1,000 W device running for one hour uses 1 kWh. So does a 100 W device running for ten hours. Multiply the kWh by your rate and you have the cost.
What rate should I use?
The most accurate number is on your own electricity bill. Divide the total charge by the kWh used to get your all-in rate, including delivery fees and taxes. Rates vary a lot between states, utilities and plans, and some plans charge different rates at different times of day.
If you don't have a bill handy, the calculator's default of $0.18 per kWh is close to the US average. The U.S. Energy Information Administration's Short-Term Energy Outlook forecasts an average residential price of about 18 cents per kWh for 2026.
Worked examples
All at $0.18 per kWh:
| Device | Calculation | Per day | Per month (30 days) |
|---|---|---|---|
| 1,500 W space heater, 4 hours a day | 1,500 × 4 ÷ 1,000 = 6 kWh | $1.08 | $32.40 |
| 60 W laptop, 8 hours a day | 60 × 8 ÷ 1,000 = 0.48 kWh | about 9¢ | about $2.59 |
| Device averaging 50 W around the clock | 50 × 24 ÷ 1,000 = 1.2 kWh | about 22¢ | about $6.48 |
The space heater and the laptop show why watts alone don't tell you much. A high-wattage device used briefly can cost less than a low-wattage one that never switches off.
Appliances that cycle on and off
Refrigerators, freezers, air conditioners and anything with a thermostat don't draw their full rated watts all the time. Multiplying the label watts by 24 hours will overestimate their cost. Better options:
- Use the EnergyGuide label. In the US, many new appliances, including refrigerators and freezers, carry a yellow EnergyGuide label with an estimated yearly kWh figure. Switch the calculator to "Yearly kWh" and enter it. For example, 450 kWh a year × $0.18 = $81 a year.
- Measure it. A plug-in watt meter between the outlet and the appliance shows the kWh actually used over a day or a week.
- Use an average. If you know the average draw across a full day, enter that with 24 hours. Our refrigerator runtime guide explains how to find it.
How much does it cost to charge a power station?
Very little. Charging from the wall loses some energy as heat in the charger, so the wall supplies a bit more than the battery stores:
Assuming 85% efficiency, a 1,024 Wh power station takes about 1.2 kWh from the wall for a full charge (1,024 ÷ 0.85 ÷ 1,000). At $0.18 per kWh that's about 22¢. Real efficiency varies by model and charging speed, so treat 85% as an estimate. Charging from solar panels costs nothing per charge once you own the panels. The solar panel size calculator shows how many panel watts you need.
Frequently asked questions
How do I convert watts to kWh?
Multiply the watts by the hours of use, then divide by 1,000. A 200 W device running for 5 hours uses 200 × 5 ÷ 1,000 = 1 kWh. If watts and watt-hours are getting mixed up, read watts vs. watt-hours.
Why is my bill higher than the calculator suggests?
Common reasons are fixed monthly charges that don't depend on usage, tiered or time-of-use rates, devices running longer than you think, and standby power from electronics that are "off" but still plugged in. A watt meter on the suspect device usually settles it.
Does running things from a power station save money?
Not when you charge it from the grid. You pay for the electricity plus the charging and inverter losses, and the battery wears a little with each cycle. Power stations are about having power when and where the grid isn't available. Charged from solar, the energy itself is free, but the panels and battery cost money up front.