About the Amp Hours Calculator
Amp-hours from current and runtime, or the runtime a given capacity gives.
Also known as: ah calculator, battery amp hours, capacity from current, battery runtime ah.
How to use this calculator
- Enter calculate, usable capacity and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
Ah = current × hours ÷ usable fraction
Worked example
Using the values pre-filled in the calculator above:
- Calculate: Amp-hours
- Current draw = 5 A
- Runtime = 10
- Usable capacity = 80 %
the calculator returns:
- Capacity required: 62.5 Ah
- Usable capacity needed: 50 Ah
- At 12 V: 0.75 kWh
- 100 Ah batteries needed: 1