About the mAh to Wh Converter
This mAh to Wh converter changes a battery capacity between milliamp-hours, amp-hours and watt-hours at the battery’s nominal voltage. Milliamp-hours tell you how much charge a battery stores, but watt-hours tell you how much energy it holds, which is what actually matters when you compare batteries of different voltages, size a power bank, or work out how long a device will run.
It is handy for phone and laptop owners comparing power banks, drone and RC hobbyists sizing LiPo packs, campers planning a portable power station, and travellers checking whether a battery is within the US TSA limit of 100 Wh per spare lithium-ion battery in carry-on bags (101–160 Wh needs airline approval).
Use the nominal cell voltage printed on the battery — 3.6 V or 3.7 V for most single lithium-ion cells, 3.85 V for many modern phone cells, 7.4 V/11.1 V for 2S/3S packs, 12.8 V for LiFePO₄ and 12 V for lead-acid. Power banks rate capacity at the internal cell voltage (usually 3.7 V), not the 5 V USB output, so real delivered energy is lower; the runtime estimate includes an efficiency factor for that.
With the default inputs, the energy capacity is 37 Wh. Change any value above to recalculate instantly.
How to use the mah to wh converter
- 1Enter the capacity printed on the battery and pick its unit.
- 2Enter the nominal voltage (3.7 V for most lithium-ion cells and power banks).
- 3Optionally enter your device’s power draw and the expected efficiency.
- 4Read the watt-hours, mAh and the estimated runtime.
- 5Check the carry-on result before flying with a spare battery or power bank.
Formula and method
Energy equals charge multiplied by voltage. Milliamp-hours are first divided by 1,000 to give amp-hours, and amp-hours × volts = watt-hours. Going the other way, divide watt-hours by the voltage to get amp-hours and multiply by 1,000 for mAh. One watt-hour is 3,600 joules, or 3.6 kJ.
The runtime estimate multiplies the rated energy by a conversion efficiency (to cover voltage-converter, inverter and wiring losses and the fact that batteries are rarely drained to zero) and divides by the device’s average power draw. The conversion uses the nominal voltage; real voltage sags as the battery discharges, so treat results as estimates.
- mAh
- Charge capacity in milliamp-hours
- V
- Nominal battery voltage
- Wh
- Energy capacity in watt-hours
- η
- Conversion efficiency (0–100%)
Worked examples
10,000 mAh power bank at 3.7 V
10,000 mAh = 10 Ah, and 10 Ah × 3.7 V = 37 Wh. At 85% efficiency about 31.45 Wh reaches the device, so a 10 W load runs for roughly 3.1 hours. 37 Wh is well under the 100 Wh carry-on limit.
Phone battery of 5,000 mAh at 3.85 V
Many phones use 3.85 V cells: 5 Ah × 3.85 V = 19.25 Wh. With no load entered, the runtime estimate is skipped.
99.5 Wh power bank (3.6 V cells) to mAh
Dividing 99.5 Wh by 3.6 V gives 27.64 Ah, or about 27,639 mAh at the cell voltage — which is why carry-on power banks top out at roughly 27,000 mAh (100 Wh ÷ 3.6–3.7 V).
Frequently asked questions
How do I convert mAh to Wh?+
Multiply the mAh rating by the battery voltage and divide by 1,000. A 3,000 mAh battery at 3.7 V holds 3,000 × 3.7 ÷ 1,000 = 11.1 Wh.
Why is Wh better than mAh for comparing batteries?+
mAh measures charge and ignores voltage, so a 2,000 mAh 12 V battery holds far more energy than a 2,000 mAh 3.7 V cell. Watt-hours include voltage and measure actual energy, so they compare fairly across battery types.
Why does my power bank deliver less than its mAh rating?+
Power banks quote capacity at the internal cell voltage (about 3.7 V) but output 5 V or more over USB, and the boost converter loses 10–20% as heat. A 10,000 mAh bank typically delivers only about 6,000–6,500 mAh at 5 V.
What is the battery limit for flying?+
In the US, TSA limits spare lithium-ion batteries to 100 Wh each in carry-on bags; with airline approval you may carry up to two spares of 101–160 Wh. Spare lithium batteries are not allowed in checked luggage.
What voltage should I use for a lithium battery?+
Use the nominal voltage, not the full-charge voltage: 3.6–3.7 V per Li-ion/LiPo cell (some phone cells 3.85 V), 3.2 V per LiFePO₄ cell, and multiply by the number of cells in series for a pack.