SoupCalc

Battery Energy to Ampere-Hour Capacity Calculator

Battery Watt-Hours to Ampere-Hours

This calculator converts a battery energy rating in watt-hours (Wh) into charge capacity in ampere-hours (Ah) using a stated nominal voltage. It is a unit relationship for one operating-voltage assumption, not a battery runtime, health, charging, range, or safety model.

Method and formula

Electrical energy is voltage multiplied by charge capacity under the simplified rating relationship:

energy (Wh) = nominal voltage (V) × capacity (Ah)

Rearranging gives the implemented equation:

capacity (Ah) = energy (Wh) ÷ nominal voltage (V)

Both inputs must be finite and greater than zero. Use watt-hours, not watts, for energy. A watt is a rate of energy transfer; a watt-hour is an amount of energy.

Worked example

For a battery rated at 100 Wh and 12 V nominal:

100 Wh ÷ 12 V = 8.33 Ah

The interface displays 8.333 Ah to three decimal places. The value means that 100 Wh divided by the assumed 12 V corresponds to about 8.33 ampere-hours; it does not guarantee that the battery will deliver exactly that charge under every load and temperature.

How to interpret the result

Ampere-hours describe electric charge, while watt-hours describe energy. Two packs with the same Ah rating but different voltage can store different energy. For example, 10 Ah at 12 V corresponds ideally to 120 Wh, whereas 10 Ah at 24 V corresponds to 240 Wh.

Use the nominal voltage associated with the energy rating. Substituting a momentary fully charged or cutoff voltage can make the converted Ah value inconsistent with the manufacturer's rating method.

Electrical and battery limits

  • The calculator does not predict runtime. Runtime also depends on load profile, conversion losses, discharge rate, allowable depth of discharge, temperature, ageing, battery-management limits, and voltage variation.
  • Real battery voltage changes during discharge. The formula treats nominal voltage as a single representative value.
  • Series and parallel pack arrangements change voltage and charge capacity differently. Confirm whether the entered ratings apply to one cell, one module, or the complete pack.
  • Do not use this value to select conductors, protection devices, chargers, or thermal controls. Follow manufacturer specifications and qualified electrical guidance for battery-system design and safety.

Sources

Editorial record

  • Author: SoupCalc Editorial Team
  • Method review: SoupCalc Electrical Engineering Review
  • Last reviewed: August 10, 2026
  • Review scope: Wh/V/Ah relationship, positive-input validation, nominal-voltage wording, example reproduction, and safety limits