Watt-hour runtime estimator
Battery Runtime Calculator
Use this when you know the battery capacity and approximate load. It works for many battery packs, inverters, and DC/AC power setups.
Fine-tune the estimate
If you only know amp-hours, convert to watt-hours by multiplying volts × amp-hours.
Use the device’s rated watts or a measured average.
Use 80–90% for many inverter setups.
Method
How this calculator estimates it
Runtime hours = battery watt-hours × efficiency ÷ load watts.
Avoid this
Common mistakes
- Confusing amps, amp-hours, watts, and watt-hours.
- Ignoring inverter losses.
- Using peak watts instead of average watts for cycling appliances.
Before you choose
- Use watt-hours for comparison. Amp-hours alone are incomplete unless voltage is also known.
- Inverters waste some power, so AC runtime is usually lower than perfect math suggests.
- For critical loads, size with reserve capacity.
Related calculators
Helpful tools that pair with this estimate.
Backup Power
Home backup generator
Estimate the generator size you need for a house during a power outage using common household loads like refrigerators, pumps, heat, lights, and AC.
Backup PowerPower station runtime
Estimate how long a portable power station can run common devices after real-world efficiency losses.