Wh to mAh Calculator
Enter a battery energy in watt-hours and the nominal voltage to get the charge capacity in milliamp-hours — the figure printed on every power bank and battery label.
From energy to charge
Enter the watt-hour figure and the nominal voltage and the calculator returns the milliamp-hour capacity that matches the label on the battery.
Use the cell voltage
A single lithium-ion cell is about 3.7 V internally — not the 5 V USB output — so enter 3.7 V to match the mAh figure the manufacturer prints.
What does the Wh to mAh calculator do?
From watt-hours back to milliamp-hours
The Wh to mAh calculator is the inverse of the mAh to Wh conversion: it takes a battery energy in watt-hours and a nominal voltage and returns the charge capacity in milliamp-hours. Watt-hours appear on airline carry-on stickers, product spec sheets, and certification labels, while milliamp-hours are the figure consumers see on the battery itself. Because the two units describe the same battery from different angles — energy versus charge — you can move between them as long as you know the nominal voltage.
Enter the energy in watt-hours and the nominal voltage in volts to get the charge capacity in milliamp-hours instantly.
A battery's energy in watt-hours equals its charge in amp-hours multiplied by its voltage. Rearranging for charge — and converting amp-hours to milliamp-hours by multiplying by 1000 — gives the formula below.
mAh = (Wh × 1000) / VSuppose a power bank carries a 50 Wh label — the kind of figure you see on an airline carry-on sticker. To find the mAh capacity, multiply 50 by 1000 to get 50,000, then divide by the nominal voltage of 3.7 V: 50,000 ÷ 3.7 = 13,513.51 mAh, which you would normally see rounded to 13,500 mAh on the casing.
The mAh figure you get tells you how much charge the battery can deliver at its nominal voltage, and it is the number manufacturers print on the label. A result of 13,514 mAh means the pack can, in theory, deliver 13,514 milliamps for one hour — or 1,351 milliamps for ten hours — before it is empty. In practice, the mAh rating is most useful for comparing two batteries at the same voltage: a 10,000 mAh power bank at 3.7 V holds less energy than a 10,000 mAh pack at 5 V, so comparing mAh alone is meaningful only when the voltages match. For cross-voltage comparisons, go back to watt-hours. The result here is the theoretical charge assuming the cell voltage stays constant; real discharge curves cause the voltage to sag, so a device may receive slightly fewer effective milliamp-hours than the calculated figure.
The conversion is straightforward arithmetic, but two practical points affect accuracy.
mAh is only meaningful at a stated voltage
Comparing two batteries by mAh alone is misleading unless their nominal voltages match — a 10,000 mAh pack at 7.4 V stores twice the energy of a 10,000 mAh pack at 3.7 V. The nominal voltage also differs from the actual cell voltage, which sags as the battery discharges, so the mAh figure is an approximation based on the rated nominal value.