mAh to Wh Converter: Calculate Battery Capacity

How to use the mah to wh converter

1. Enter the numeric value you want to convert.
2. Select the conversion direction: mAh to Wh or Wh to mAh.
3. Set the nominal voltage of the battery (default is 3.7 V for lithium-ion).
4. Read the result below along with a reference table for other common voltages.

How the conversion works

Amp-hours measure electric charge, while watt-hours measure energy. To move between them you need the battery's nominal voltage. The formulas used by this mah to wh calculator are straightforward:

• mAh to Wh: Wh = mAh / 1000 * V
• Wh to mAh: mAh = Wh / V * 1000

For example, a 3000 mAh phone battery at 3.7 V stores 3000 / 1000 * 3.7 = 11.1 Wh. Reversing that, 11.1 Wh at 3.7 V gives 11.1 / 3.7 * 1000 = 3000 mAh. Voltage matters because two batteries with identical mAh ratings store different amounts of energy if their voltages differ.

Common battery voltages reference

The table below shows how 1000 mAh translates to watt-hours at several standard nominal voltages. Use it as a quick lookup when comparing cells.

Airline carry-on battery limits

Airlines regulate spare lithium batteries by energy content in watt-hours, not by mAh. Under IATA guidance, spare batteries up to 100 Wh are generally allowed in carry-on luggage without approval. Batteries between 100 Wh and 160 Wh usually need airline approval, and anything above 160 Wh is typically forbidden on passenger aircraft. Airlines and countries decide for themselves and rules vary, so always check with your carrier.

This is why converting mah to watt hours is essential before flying. A 20000 mAh power bank at 3.7 V holds 74 Wh, which is under the 100 Wh limit. A 30000 mAh pack at 3.7 V yields 111 Wh, crossing into the restricted range. The tool compares the exact, unrounded energy with those limits: 27027 mAh at 3.7 V is 99.9999 Wh, while 27028 mAh is 100.0036 Wh. Always check the printed Wh rating on your device or use this tool to calculate battery capacity wh before packing.

Why mAh alone is misleading

Manufacturers often advertise mAh because larger numbers look impressive, but mAh only tells part of the story. A 5000 mAh battery at 3.7 V stores 18.5 Wh, while a 5000 mAh battery at 7.4 V stores 37 Wh, exactly double the energy. When comparing devices with different internal voltages, always convert to watt-hours first.

This distinction matters when sizing solar setups, choosing drone batteries, or comparing power banks. If you also need to estimate how long a battery will power a specific load, pair this result with a battery runtime calculator to factor in current draw and efficiency losses.

Practical tips for accurate results

Use the nominal voltage printed on the cell or pack rather than the fully charged voltage. A single lithium-ion cell charges to 4.2 V but has a nominal rating of 3.6 V or 3.7 V depending on chemistry. Using 4.2 V will overstate the energy capacity.

For multi-cell packs, multiply the single-cell nominal voltage by the series count. A 3S pack uses three cells in series, so its nominal voltage is 3 x 3.7 = 11.1 V. Parallel cells increase mAh without changing voltage. Keep these rules in mind when working with RC hobby packs or laptop replacement batteries.

Worked examples