mAh vs Wh: how to actually compare battery sizes
Why mAh doesn't compare across devices, and the number that does.
By Let’s Compare · 1 min read · Updated September 24, 2026
Phone batteries are quoted in mAh, laptop and handheld batteries in Wh, and you can't compare the two directly. Converting to one unit fixes that, and it takes a single multiplication.
mAh vs Wh
| mAh | Wh | |
|---|---|---|
| Measures | Charge | Energy |
| Depends on voltage? | No (charge only) | Yes (energy) |
| Compare across devices? | No | Yes |
| Convert | — | mAh × V ÷ 1000 |
Charge vs energy
mAh (milliamp-hours) measures electrical charge, meaning how much current a battery can supply over time. Charge alone doesn't give you energy, because energy also depends on voltage. Wh (watt-hours) measures actual energy, which makes it the fairer number: watt-hours = amp-hours × voltage. A 5,000 mAh cell at 3.8 V holds about 19 Wh.
Why mAh misleads across devices
Voltage varies. A phone battery runs around 3.7–3.8 V, while a laptop battery might be 11–15 V. So a laptop's '6,000 mAh' holds far more energy than a phone's '6,000 mAh', because each mAh is delivered at a higher voltage. Line up a phone and a laptop on mAh and you're comparing charge, not energy. The comparison is meaningless.
Converting to watt-hours
If a battery lists mAh and voltage, multiply them and divide by 1,000 to get Wh (e.g. 5,000 mAh × 3.8 V ÷ 1,000 = 19 Wh). Now any two batteries sit on the same scale. Capacity still isn't battery life, mind you: an efficient chip and screen can outlast a bigger battery that's feeding hungry hardware.
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Sources & further reading
The facts and figures in this article come from the references below (some of them not in English), so you can check them yourself.
- Ampere-hour — Wikipedia
- Kilowatt-hour — Wikipedia