mAh to Watt-Hours Calculator
Capacity in milliamp-hours only tells half the story — energy needs the voltage too. Convert mAh to watt-hours or back again, and compare batteries fairly, size power banks, or check airline limits.
Use the pack's nominal voltage — a single Li-ion cell is ~3.7 V, a USB power bank cell the same before boosting to 5 V.
Formula & how it works
Energy is Wh = mAh ÷ 1000 × V. Going back, mAh = Wh × 1000 ÷ V. Amp-hours are simply mAh ÷ 1000.
Worked example
A 3000 mAh cell at 3.7 V holds 3 × 3.7 = 11.1 Wh. A 10000 mAh power bank cell at the same voltage is 37 Wh — comfortably under the usual 100 Wh airline limit. Converting back, 37 Wh at 3.7 V returns 10000 mAh.
Why watt-hours matter
mAh hides the voltage
Milliamp-hours count charge, not energy, so they only compare fairly between batteries at the same voltage. A 5000 mAh 3.7 V cell and a 5000 mAh 7.4 V pack hold very different amounts of energy. Converting both to watt-hours puts them on equal terms.
The power bank surprise
Power banks are labeled in mAh at the internal cell voltage of 3.7 V, but they output 5 V over USB. After the boost and its losses, the usable energy at 5 V is less than the headline mAh implies — which is why a "10000 mAh" bank charges a 3000 mAh phone fewer times than you might expect. Watt-hours make that clearer.
Travel rules run on Wh
Airlines cap lithium batteries by watt-hours, commonly 100 Wh in carry-on without special approval and 160 Wh with it. Since packs are marked in mAh, converting at the cell voltage is the quick way to confirm a battery is allowed before you reach the gate.