Amp hours to watt hours calculator

How to convert Ah or mAh to Wh

For example, a 100 Ah rating at 12.8 V gives 1,280 Wh, or 1.28 kWh, on a nominal-rating basis. The same 100 Ah at 25.6 V gives 2,560 Wh. That is why two amp-hour numbers should not be compared as energy until their voltages are known.

A smaller illustrative pack rated 10,000 mAh at 3.7 V represents 10 Ah × 3.7 V = 37 Wh. Multiplying 10,000 directly by 3.7 would miss the milliamp-to-amp conversion and inflate the answer by a factor of 1,000.

Amp-hours describe charge capacity. Watt-hours describe energy; watts describe power. Dividing a Wh figure by a duration would introduce a new assumption about power over that time. This page keeps the calculation at the stated nominal-energy level.

Use voltage and capacity from the same rating

Start with the manufacturer’s specification for the battery or complete pack you are describing. A cell’s voltage, a finished pack’s voltage, a charging voltage and a regulated output voltage can refer to different boundaries. Mixing one boundary’s amp-hour figure with another boundary’s voltage produces a different calculation.

If a label already supplies the complete pack’s nominal voltage and Ah, leave the bank option off. Do not multiply by its internal cell count again. If you are accounting for several identical rated units, enter one unit’s values and enable the bank fields instead.

Energizer’s battery glossary defines delivered energy using amp-hour capacity and average discharge voltage, and explains that a capacity rating has specified test conditions. This tool uses your nominal voltage as a simplified rating basis. It does not integrate an actual discharge curve or replace the manufacturer’s published energy figure.

Series and parallel change different totals

For identical units in an ideal accounting model, series units add nominal voltage while parallel strings add amp-hour capacity. Mastervolt’s battery FAQ explains the distinction between series, parallel and combined arrangements. The equations here describe the totals; they do not determine which arrangements a particular product permits.

“Two by two” means two units in each of two parallel strings: four units altogether. It does not mean two units total. Each string is assumed to contain the same number and rating of units.

The ideal nominal energy stays 5.12 kWh because the same four unit ratings are being added. The voltage and Ah totals differ. Equal energy does not make these arrangements interchangeable with a load or charger.

What the nominal total leaves out

The result does not apply a usable-capacity percentage, discharge limit, converter loss or aging factor. Adding an arbitrary “efficiency” value would make the number look more specific without showing that it describes your equipment or operating conditions. Use documented performance information for those separate questions.

A bank can also have limits unrelated to its total nominal Wh. Current capability, protection behavior, allowed connections and equipment compatibility cannot be recovered from voltage and capacity alone. This calculator therefore supplies no assembly instructions or safe-connection verdict.

For power measured over several operating periods, the changing-load kWh calculator uses real watts and elapsed time instead. For a current calculation, the watts to amps calculator uses power, voltage and the applicable electrical assumptions. The nameplate guide helps keep input and output ratings distinct.

A complete tool, free to use

Capacity units preserve the physical value when switched. The bank option keeps the per-unit basis visible, and Copy includes both the ratings and the limitations of the calculation. Reset returns to an empty single-unit form. All arithmetic runs in your browser.

Find other tools in the electrical directory. If the calculator or explanation needs a correction, email contact@wattstoamps.app.