Guide

Comparing batteries: mAh, Ah and Wh

mAh is the number on the packaging, Wh the number that actually allows batteries to be compared.

Charge is not energy

Ampere hours and milliampere hours measure charge: how much current flows over a given time. Watt hours measure energy. The two are linked through voltage by the formula Wh = Ah × volts. Without a voltage figure, a mAh number is not an amount of energy.

Why the packaging figure misleads

A 5000 mAh battery at 3.7 V stores 18.5 Wh. A 4500 mAh battery at 5 V stores 22.5 Wh. So the battery with the smaller mAh figure holds more energy because its voltage is higher. This exact case occurs regularly when comparing single cells, power banks and laptop batteries.

Conversions within charge

Within charge everything is a pure factor: 1 Ah is 1000 mAh, 1 Ah is 3600 coulombs, 1 mAh is 3.6 coulombs. These conversions are exact because the coulomb is defined via the ampere-second. Difficulties only appear once energy enters, because then voltage comes into play.

What the Wh figure does not tell you

The Wh figure also describes energy content, not usable energy. Conversion losses, discharge curve, temperature and ageing reduce what actually arrives. Power banks additionally often state cell capacity while the 5 V output is lower. Wh is the right quantity for comparing form factors; for a runtime prediction it remains an estimate.

Matching conversions

Milliampere hour to Ampere hourmAh → AhElectric charge Ampere hour to Milliampere hourAh → mAhElectric charge Ampere hour to CoulombAh → CElectric charge Milliampere hour to CoulombmAh → CElectric charge Coulomb to Ampere hourC → AhElectric charge

Matching tables

TableBattery capacity: mAh and Wh

Unit family: Electric charge

Common questions

How do you convert mAh to Wh?

Wh = mAh ÷ 1000 × volts. Without the nominal voltage the conversion is impossible.

How many coulombs are one ampere hour?

1 Ah = 3600 C, because one hour has 3600 seconds.

Is 2000 mAh the same as 2 Ah?

Yes, 1 Ah equals 1000 mAh.

Why does my power bank have less Wh than advertised?

Many power banks state cell capacity. At the 5 V output the usable energy is lower, and conversion losses add to that.

Sources

BIPM SI BrochureSI base units, prefixes and official SI context.NIST Guide to SI Appendix BNIST conversion-factor method and non-SI factors.

When not to use

Do not use as the sole basis for official, medical, safety-critical or contractual decisions.

Citation

Citation note: UnitCloud, guide, sources reviewed: September 2026. Source basis: BIPM SI Brochure · NIST Guide to SI Appendix B.