Electrical units and conversion

mAh to Wh calculator

Convert milliamp-hours to watt-hours — and watt-hours back to mAh — at the voltage the battery is rated at. Useful for phones, power banks and laptop batteries.

How do you convert mAh to Wh?

Multiply mAh by the battery's voltage and divide by 1,000: Wh = mAh × V ÷ 1,000. A 10,000 mAh power bank rated at 3.7 V holds 37 Wh. The reverse is mAh = Wh × 1,000 ÷ V, so 37 Wh at 3.7 V is 10,000 mAh. Voltage is not optional: mAh measures charge, and the same mAh figure is a different amount of energy at a different voltage.

Your inputs

Conversion

Capacity

Voltage

Required. Use the voltage the mAh rating was measured at — usually the cell's nominal voltage printed on the battery or label.

Voltage presets

3.7 V: Nominal voltage commonly printed on Li-ion power banks and phone cells. No single voltage is correct for every battery.

10,000 mAh × 3.7 V ÷ 1,000

Exact given your inputs

Energy: 37 Wh
Amp-hours: 10 Ah
Voltage: 3.7 V
In kWh: 0.037

mAh alone does not tell you the energy

mAh measures charge. Energy needs voltage too: Wh = mAh × V ÷ 1,000. The same 10,000 mAh is 37 Wh at 3.7 V but 50 Wh if it were rated at 5 V — which is why the rated voltage matters.

Method

Wh = mAh × V ÷ 1,000
mAh = Wh × 1,000 ÷ V
Ah = mAh ÷ 1,000

Computed by conversionEngine-1.0.0. Zero or negative voltage is rejected.

Assumptions

V is the voltage the mAh rating refers to — normally the cell's nominal voltage.
Result is nominal stored energy, not energy delivered after conversion losses.
Display rounds to at most 4 decimals (2 above 100).

What can change the result?

Power banks lose energy boosting cell voltage up to USB output, so you get fewer Wh out than stored.
Capacity falls with age, cold and high discharge rates.
Using 5 V instead of the cell voltage overstates the energy of a cell-rated mAh figure.

Which voltage should you use?

Use the voltage the mAh number was measured at. A power bank's advertised mAh is almost always the capacity of its internal lithium cells at their nominal voltage (typically 3.6–3.7 V), while it delivers power at 5 V or higher over USB. Those are not the same basis: the same pack's capacity expressed at 5 V output would be a smaller mAh number, and conversion losses reduce it further. Many power banks print the Wh figure directly — when they do, that is the number to trust.

What each preset voltage represents. None of them is correct for every battery.
Voltage	What it represents
3.6 V	Nominal voltage of many lithium-ion cells
3.7 V	Nominal voltage commonly printed on Li-ion power banks and phone cells
3.85 V	Nominal voltage of some higher-voltage phone cells
5 V	Standard USB output voltage, not the cell voltage
11.1 V	Nominal voltage of a 3-cell lithium-ion laptop pack

Examples

Phone battery: 5,000 mAh at 3.85 V = 19.25 Wh.
Power bank: 20,000 mAh at 3.7 V = 74 Wh.
Laptop pack: a 99 Wh battery at 11.1 V = 8,918.92 mAh.

mAh to Wh reference table

Wh = mAh × V ÷ 1,000, computed by conversionEngine-1.0.0. Nominal stored energy.
Capacity	3.6 V	3.7 V	3.85 V	5 V
3,000 mAh	10.8 Wh	11.1 Wh	11.55 Wh	15 Wh
5,000 mAh	18 Wh	18.5 Wh	19.25 Wh	25 Wh
10,000 mAh	36 Wh	37 Wh	38.5 Wh	50 Wh
20,000 mAh	72 Wh	74 Wh	77 Wh	100 Wh
26,800 mAh	96.48 Wh	99.16 Wh	103.18 Wh	134 Wh

Watt-hours and flying with lithium batteries (US)

US passenger rules are written in watt-hours, which is one reason people convert mAh to Wh. Per the FAA's PackSafe guidance (checked 3 October 2026):

Source: FAA PackSafe — Lithium Batteries (faa.gov/hazmat/packsafe/lithium-batteries), as checked 3 October 2026. General US passenger rules; individual airlines may set stricter limits, including on how many power banks you may carry. Check with your airline before flying.
Lithium-ion rating	General FAA rule
Up to 100 Wh per battery	Allowed; spares (including power banks) in carry-on baggage only
Over 100 Wh up to 160 Wh	Only with airline approval; maximum two spare batteries per person
Over 160 Wh	Not covered by the passenger allowances above

For larger batteries rated in amp-hours, use Ah to Wh, Wh to Ah, Ah to kWh or kWh to Ah.