Battery Runtime Calculator
Runtime = usable energy × efficiency ÷ load
Estimate operating time using usable watt-hours and a constant load.
Formula
Runtime = usable energy × efficiency ÷ load
Worked example
Usable battery energy: 1000 Wh
Load power: 100 W
System efficiency: 90 %
With these inputs, the result is 9 hours.
How to use this calculator
- Identify the quantity you want to calculate.
- Enter your measurements in the units shown on each field.
- Read the result, which updates as you change the inputs.
- Check the assumptions below before applying the result.
Assumptions and limits
Use usable battery energy, not nameplate energy. Constant load and fixed efficiency are assumed.
Precision and checking
Results are rounded for display. Use the most accurate measurements available, and avoid rounding your inputs unnecessarily. Extra decimal places in a result do not make an estimate more reliable.
To check a result, substitute the same input values into the formula shown above. Change one value at a time to understand how the quantity responds.
Frequently asked questions
What assumptions does this calculation use?
Use usable battery energy, not nameplate energy. Constant load and fixed efficiency are assumed.
Are my inputs sent to a server?
No. The calculation runs locally in your browser. The result updates as you edit the inputs.
Sources & references
- NIST Guide to the SI — National Institute of Standards and Technology
