Convert mAh into useful numbers.
Get Wh, Ah and theoretical runtime from the capacity printed on a phone, power bank, sensor or other small battery.
What does this battery really hold?
Convert mAh into Wh and estimate theoretical runtime from the average current your device draws.
The mAh calculator formulas
mAh is a charge rating. To compare batteries by stored energy, include voltage. To estimate runtime, compare capacity with the average current the device draws.
For a battery pack, use its nominal pack voltage rather than the voltage of a single cell. For real runtime, leave room for conversion loss and the device cutoff voltage.
mAh, Ah, Wh and voltage
- mAh
- Milliamp-hours measure charge capacity. They are common on small electronics and battery packs.
- Ah
- Amp-hours are the same charge unit at a larger scale: 1 Ah equals 1,000 mAh.
- Wh
- Watt-hours measure energy. They are better for comparing batteries with different voltages.
- Voltage
- Voltage converts charge into energy. A higher-voltage battery can store more Wh at the same mAh rating.
FAQ
How do I convert mAh to Wh?
Multiply battery capacity in mAh by nominal voltage in V, then divide by 1000: Wh = mAh × V ÷ 1000.
How do I calculate runtime from mAh?
Divide battery capacity in mAh by average device current in mA: runtime hours ≈ mAh ÷ mA.
Why do I need voltage to calculate Wh?
mAh measures charge, while Wh measures energy. Voltage is the bridge between them, so the same mAh at different voltages represents different energy.
Is the runtime estimate exact?
No. It is a theoretical estimate. Conversion efficiency, temperature, battery age, cutoff voltage and changing device load will reduce or change real runtime.