mAh to Wh Converter (and Wh to mAh)
mAh to Wh Converter (and Wh to mAh)
Convert battery capacity between mAh, Ah and watt-hours at a stated cell voltage, with the energy in kWh and joules — and what a power bank really delivers at 5 V.
Battery capacity
A 10,000 mAh power bank of 3.7 V cells, 85% efficient at 5 V out
Charge, voltage and energy
- mAh
- charge the cell can deliver: milliampere-hours
- V
- nominal voltage of the cell or pack — 3.7 V for most lithium-ion
- Wh
- energy: what actually powers something, and what airlines limit
- η
- efficiency of the converter between the cell and the output
Worked example
A 10,000 mAh power bank of 3.7 V cells, 85% efficient at 5 V out
Wh = 10,000 × 3.7 ÷ 1,000 = 37 Wh (133,200 J)
At 85% through the boost converter: 31.45 Wh reaches the USB port
At 5 V that is 31.45 ÷ 5 = 6.29 Ah = 6,290 mAh — not the 10,000 mAh on the box
Under IATA's 100 Wh threshold, so it travels in carry-on baggage
Common batteries in mAh and Wh
| Battery | Capacity | Nominal voltage | Energy | At 5 V, 85% |
|---|---|---|---|---|
| Phone battery | 5,000 mAh | 3.85 V | 19.25 Wh | 3,272 mAh |
| Power bank | 10,000 mAh | 3.7 V | 37.0 Wh | 6,290 mAh |
| Power bank | 20,000 mAh | 3.7 V | 74 Wh | 12,580 mAh |
| Laptop battery | 6,000 mAh | 11.1 V | 66.6 Wh | — |
| E-scooter battery | 20,000 mAh | 48 V | 960 Wh | — |
mAh, Ah and watt-hours
Milliampere-hours measure charge: how many milliamps the cell can push for how many hours. Watt-hours measure energy, which is charge multiplied by the voltage it comes out at. That is the whole conversion: Wh = mAh × V ÷ 1,000. A 10,000 mAh power bank built from 3.7 V lithium cells holds 37 Wh, or 133,200 joules; the same 10,000 mAh at 48 V, as on an e-bike, holds 480 Wh.
Why your power bank never gives the number on the box. The 10,000 mAh is measured at the cells’ 3.7 V. Your phone is charged at 5 V (or higher, over USB-C). Converting from 3.7 V to 5 V loses energy — 10–15% in a good boost converter, more in a cheap one — and the charge at the higher voltage is smaller in proportion. So 37 Wh of cells deliver about 31.45 Wh at the port, which at 5 V is 6,290 mAh: roughly 63% of the printed figure, before the losses in the phone’s own charging circuit. Two thirds is the realistic expectation, and it is why a 10,000 mAh bank does not charge a 5,000 mAh phone twice.
Nominal voltage is an average. A lithium-ion cell starts near 4.2 V and is empty around 3.0 V; its “3.7 V” (sometimes 3.6 or 3.85 V) is the average under load. LFP cells are 3.2 V, NiMH 1.2 V, and a lead-acid battery 12 V per six cells. Packs multiply: three 3.7 V cells in series make an 11.1 V laptop pack, so 6,000 mAh becomes 66.6 Wh. Cells in parallel add mAh at the same voltage.
Watt-hours are what get regulated and what size systems. IATA’s traveller guidance puts the line for spare lithium batteries and power banks at 100 Wh for carry-on, with 100–160 Wh needing the airline’s approval; from 2026 it also limits passengers to two power banks and forbids recharging them in flight. Airlines and countries add their own rules, so check before flying. For anything bigger — an inverter battery, a solar bank — energy is again the useful unit: the inverter backup time calculator turns the same Ah × V into hours of backup, and the battery life calculator into runtime for a given load.
Frequently asked questions
How do I convert mAh to Wh?
Multiply by the nominal voltage and divide by 1,000. 10,000 mAh at 3.7 V is 37 Wh.
How do I convert Wh to mAh?
Multiply by 1,000 and divide by the voltage. 37 Wh at 3.7 V is 10,000 mAh; the same 37 Wh at 11.1 V is 3,333 mAh.
Why does my 10000mAh power bank only charge my phone once and a half?
Because the 10,000 mAh is at the cells’ 3.7 V. After the boost converter to 5 V you have about 6,290 mAh at 5 V, and your phone’s own charging circuit loses a little more.
What is the 100Wh airline limit?
IATA’s guidance allows spare lithium batteries and power banks up to 100 Wh in carry-on baggage; 100–160 Wh requires the airline’s approval, and above 160 Wh they are not accepted. From 2026 no more than two power banks per passenger, and no charging on board.
Is a higher mAh battery always better?
Only at the same voltage. Compare watt-hours: a 3,000 mAh 11.1 V pack holds far more energy than a 6,000 mAh 3.7 V one.
Related calculators
References
- IATA. Lithium Batteries — travelling with batteries and Guidance to Operators: Power Banks: up to 100 Wh is generally allowed in carry-on baggage, 100–160 Wh needs the airline’s approval, and from 2026 no more than two power banks per person, not to be recharged on board.
- Battery University. BU-409: Charging Lithium-ion: a full charge at 0.5C–1C takes about 2–3 hours; charge efficiency is about 99%; the cell is full when the current falls to 3–5% of the Ah rating.
- JinkoSolar. Tiger Neo N-type 72HL4-(V) 580–605 W datasheet, model JKM590N: 590 W, Voc 52.63 V, Isc 14.13 A, Vmp 43.71 V, Imp 13.50 A, temperature coefficient of Voc −0.25%/°C, 2,278 × 1,134 mm, 22.84% efficient.