mAh to Wh Calculator
Enter a battery capacity in mAh and the pack voltage to get the energy in watt-hours and kilowatt-hours — the real measure of how much a power bank holds.
Watt-hours and kilowatt-hours
Enter the capacity in mAh and the voltage and the calculator returns the energy in watt-hours (Wh) and the same energy in kilowatt-hours (kWh).
Use the cell voltage
A single lithium-ion cell is about 3.7 V — use the nominal pack voltage, not the 5 V USB output, to match the Wh figure on the label.
What does the mAh to Wh calculator do?
From charge to real energy
The mAh to Wh calculator turns a battery's milliamp-hour rating and its voltage into watt-hours, the true measure of stored energy. Capacity in mAh alone only describes electric charge — two packs with the same mAh but different voltages hold different amounts of energy. By combining the capacity with the nominal voltage, watt-hours let you compare power banks fairly, estimate how many times a device can be recharged, and check the figure airlines care about. It is the number printed in fine print on every power bank and the one that decides whether a battery is allowed in carry-on luggage.
Enter the capacity in mAh and the pack voltage in volts to get the energy in watt-hours and kilowatt-hours instantly.
Watt-hours are the capacity in milliamp-hours multiplied by the voltage and divided by 1000, because a milliamp-hour is a thousandth of an amp-hour.
Wh = (mAh × V) / 1000Suppose you have a 10,000 mAh power bank built from lithium-ion cells at a nominal 3.7 V. Multiply the capacity by the voltage to get 10,000 × 3.7 = 37,000 milliwatt-hours, then divide by 1000 to convert to watt-hours: 37 Wh. Divide once more by 1000 and you get 0.037 kWh. To get the energy in kilowatt-hours directly, divide the watt-hours by 1000.
The watt-hour figure tells you how much energy the pack actually stores. The 37 Wh power bank above sits comfortably under the airline carry-on limit, which is usually quoted in watt-hours and capped around 100 Wh without special approval — so a 10,000 mAh pack at 3.7 V is fine to fly with, while a 27,000 mAh pack at 3.7 V is near the cap.
Use the nominal voltage, and expect real-world losses
Use the nominal cell voltage (about 3.7 V for lithium-ion), not the 5 V USB output — otherwise the watt-hours will be too high. The result is the energy stored in the cells; voltage conversion and heat mean a device receives somewhat less than the full Wh in practice.