mAh to Wh Calculator

What is a mAh to Wh calculator?

A mAh to Wh calculator converts a battery’s rated capacity, expressed in milliamp-hours (mAh), into the energy it stores, expressed in watt-hours (Wh). Capacity in mAh on its own only tells you how much charge a cell holds; it does not describe energy until you also account for the voltage at which that charge is delivered. Watt-hours combine both pieces of information, which is why energy ratings — and airline carry-on limits — are usually given in Wh.

This tool is handy when comparing power banks, laptop batteries, and lithium cells that quote different voltages, because two packs with the same mAh figure can store very different amounts of energy.

How does it work?

Energy is charge multiplied by voltage. Battery capacity in milliamp-hours is a charge figure, so multiplying it by the pack voltage gives milliwatt-hours; dividing by 1000 converts that to watt-hours:

Here $Wh$ is the stored energy in watt-hours, $mAh$ is the capacity in milliamp-hours, and $V$ is the nominal voltage in volts. The factor of 1000 simply rescales milli-units to whole units.

How to use

1. Enter the battery capacity in milliamp-hours (mAh).
2. Enter the nominal voltage of the cell or pack in volts.
3. Read the stored energy in watt-hours. The result appears automatically once both fields are filled.

Use the nominal voltage printed on the battery — for a single lithium-ion cell that is typically 3.7 V.

Worked examples

A 3000 mAh cell at 3.7 V stores:

A 2000 mAh pack running at 5 V holds:

So even though the second pack has a lower mAh rating, its higher operating voltage means the two store nearly the same energy.

Practical notes

Because mAh alone ignores voltage, always convert to watt-hours when comparing batteries that run at different voltages, or when checking the 100 Wh airline limit for carry-on power banks. Real-world usable energy is a little lower than the nominal figure, since voltage sags as a cell discharges and some capacity is lost to internal resistance.

To work in the other direction or with related units, the Wh to Ah calculator splits energy back into charge at a given voltage, while the kWh to watts calculator and the watts to kWh calculator relate energy to power and run time.