Amp Hour Calculator

Convert amp-hours to watt-hours, kilowatt-hours, runtime, battery bank capacity, charging time, and batteries needed. This calculator is useful for solar batteries, RV batteries, marine batteries, backup batteries, off-grid systems, and portable power planning.

Calculate Amp Hours

Watt-hours = volts × amp-hours. Amp-hours = watt-hours ÷ volts.
Your result will appear here.

How the amp hour calculator works

Amp-hours to energy:
The calculator multiplies volts by amp-hours to estimate watt-hours.

Energy to amp-hours:
It divides watt-hours by volts to estimate amp-hours.

Runtime and charging:
Usable amp-hours are used to estimate runtime, required battery size, and charging time.

Why use an amp hour calculator?

An amp hour calculator helps compare batteries, estimate runtime, size battery banks, and convert between Ah, Wh, and kWh.

It can help with solar batteries, RV batteries, marine batteries, trolling motor batteries, backup power, UPS batteries, off-grid cabins, and portable power systems.

What your result means

Your result shows amp-hours, watt-hours, kilowatt-hours, usable amp-hours, usable watt-hours, usable kWh, runtime, amp-hours needed, battery bank capacity, charging time, total battery cost, and detailed load row totals.

Amp hour calculator formulas

Frequently asked questions

What is an amp-hour?

An amp-hour is a measure of current over time. A 100Ah battery can theoretically provide 100 amps for 1 hour, 10 amps for 10 hours, or 1 amp for 100 hours before losses and limits.

How do I convert amp-hours to watt-hours?

Multiply amp-hours by voltage. For example, 100Ah at 12V equals 1,200Wh.

How do I calculate amp-hours needed?

Multiply load watts by runtime hours, then divide by battery voltage and efficiency. Add reserve capacity if you do not want to drain the battery too far.

Why does voltage matter for amp-hours?

Amp-hours do not show total energy by themselves. A higher-voltage battery with the same amp-hour rating stores more watt-hours.