Wh to mAh Calculator
Convert energy in watt-hours (Wh) to electric charge in milliamp-hours (mAh). Enter the energy and the voltage, and press Calculate — the charge is Q(mAh) = 1000 × E(Wh) / V(V). Everything runs locally in your browser.
Enter the energy in Wh
Type the energy in watt-hours (Wh) — for example 18.5 for a typical 5000 mAh phone battery label or 100 for the largest power bank allowed in carry-on luggage.
Enter the voltage in V
Type the voltage in volts (V): 3.7 V for a single lithium-ion cell, 5 V for USB, 12 V for a lead-acid battery. The voltage must be greater than zero because the charge divides by it.
Press Calculate, read mAh
The charge appears in milliamp-hours (mAh). Press Reset at any time to clear the inputs and the result and start over.
Wh to mAh formula
- How do I convert Wh to mAh?
- The charge Q in milliamp-hours is equal to 1000 times the energy E in watt-hours divided by the voltage V in volts: Q(mAh) = 1000 × E(Wh) / V(V). So milliamp-hours is 1000 times watt-hours divided by volts.
- Example: how many mAh is 10 Wh at 5 V?
- Q = 1000 × 10 Wh / 5 V = 2000 mAh. At the 3.7 V nominal voltage of a single lithium-ion cell, the same 10 Wh equals 1000 × 10 / 3.7 ≈ 2702.7 mAh.
- Why does the voltage matter?
- mAh measures charge, not energy. The same 100 Wh pack is labeled 27027 mAh at 3.7 V but only 8333 mAh at 12 V — for a fixed amount of energy, the milliamp-hour figure scales inversely with the voltage it is quoted at.
- Which voltage should I enter for a battery pack?
- Use the pack nominal voltage: about 3.7 V per lithium-ion cell in series (11.1 V for a 3S pack), 2 V per lead-acid cell (12 V for a car battery), or 5 V for USB output ratings. Capacity labels are usually quoted at the nominal voltage.
- Why is zero volts rejected?
- The formula divides the energy by the voltage, so V = 0 is division by zero and has no physical meaning — the calculator shows an error instead of a result. Any voltage strictly greater than zero is accepted, and 0 Wh is a valid input that yields 0 mAh.
Privacy: every calculation runs in your browser tab — no value you type is sent anywhere. Results are ideal DC conversions; real battery capacity differs with discharge rate, temperature, and cutoff voltage.