Watts to Watt-Hours Calculator
Calculate your backup power before you buy. Use this watts to watt-hours calculator to estimate how much battery capacity a device may use over time. This is useful when sizing a portable power station, solar generator or backup battery.
Enter device wattage and runtime hours to calculate watt-hours. You can also reverse the calculation to estimate runtime from battery capacity. Results are planning estimates based on typical device wattage. Actual results may vary based on device cycling, inverter losses, battery age, temperature and published specifications.
Watts to Watt-Hours Calculator
Use this calculator to convert watts and hours into watt-hours, or estimate runtime from battery capacity.
Watts vs Watt-Hours: What Is the Difference?
Watts measure how much power a device uses at a moment in time. Watt-hours measure energy used over time. A 100W device running for 5 hours uses about 500Wh.
Watt-hours = watts × hours
This is one of the most important formulas for choosing a portable power station. A battery rated at 1,024Wh has much more stored energy than a 256Wh battery, but output losses and real device behavior still matter.
Quick Examples
| Device load | Runtime | Estimated energy use |
|---|---|---|
| 10W phone charger | 5 hours | 50Wh |
| 15W Wi-Fi router | 24 hours | 360Wh |
| 60W laptop | 8 hours | 480Wh |
| 100W TV | 4 hours | 400Wh |
| 40W CPAP machine | 8 hours | 320Wh |
| 150W average refrigerator load | 10 hours | 1,500Wh |
How to Use Watt-Hours for Backup Power Planning
Start by listing every device you want to run. Estimate the watts for each device, multiply by the number of hours you need it, then add the watt-hours together. This gives a rough energy requirement before battery and inverter losses.
For AC outlets on a portable power station, plan for inverter losses. For USB or DC output, efficiency may be better, but the exact result depends on the power station and device. It is usually smart to add a reserve margin instead of planning to drain the battery completely.
Common Planning Mistakes
- Confusing watts and watt-hours: watts are power; watt-hours are energy over time.
- Ignoring inverter losses: AC output usually reduces usable battery capacity.
- Using peak watts instead of average watts: cycling appliances like refrigerators vary over time.
- Forgetting startup surge: motor loads may need extra power to start.
- No reserve margin: real outages and trips rarely match perfect calculations.
Related Calculators
- Portable Power Station Runtime Calculator
- CPAP Battery Runtime Calculator
- Refrigerator Backup Time Calculator
- Solar Charging Time Calculator
FAQ
How do you convert watts to watt-hours?
Multiply watts by hours. For example, 100 watts used for 5 hours equals 500 watt-hours.
How many watt-hours does a 60W laptop use in 8 hours?
A 60W laptop used for 8 hours uses about 480Wh before conversion losses. Actual power use depends on workload, charging state and screen brightness.
Is watt-hours the same as battery capacity?
Portable power station capacity is often listed in watt-hours. A 1,024Wh battery stores more energy than a 512Wh battery, but usable output may be lower after efficiency losses and reserve capacity.
Why is my real runtime shorter than the calculation?
Runtime can be shorter because of inverter losses, device cycling, temperature, battery age, high startup loads and manufacturer reserve capacity.
PowerStationCalc.com provides planning calculators and educational content. Calculations are based on typical device wattage and published specifications. Actual results may vary.