Use this quick battery capacity calculator to convert milliamp-hours (mAh) to watt-hours (Wh). Enter your battery capacity and voltage to get an accurate energy value.
What this mAh to Wh calculator does
Battery sizes are often listed in mAh, but shipping regulations, airline rules, and many technical specs use Wh. This tool converts mAh to Wh instantly so you can compare batteries correctly, check travel limits, and estimate run time more accurately.
mAh vs Wh: what is the difference?
mAh (milliamp-hours)
mAh tells you how much charge a battery can deliver over time. It does not directly include voltage, so it is incomplete if you want total energy.
Wh (watt-hours)
Wh measures actual energy. Because it includes voltage, it is the better value when comparing different battery chemistries or battery packs with different voltages.
How to convert mAh to Wh manually
Use this equation:
Wh = (mAh × Voltage) ÷ 1000
Example: a 10,000 mAh battery at 3.7V:
- 10,000 × 3.7 = 37,000
- 37,000 ÷ 1000 = 37 Wh
Common conversion examples
| Battery Capacity | Voltage | Energy (Wh) |
|---|---|---|
| 5,000 mAh | 3.7V | 18.5 Wh |
| 10,000 mAh | 3.7V | 37 Wh |
| 20,000 mAh | 3.7V | 74 Wh |
| 26,800 mAh | 3.7V | 99.16 Wh |
| 5,000 mAh | 5V | 25 Wh |
Why voltage matters so much
Two batteries can both be 10,000 mAh but hold different amounts of energy if voltage is different. A 10,000 mAh battery at 3.7V stores 37 Wh, while at 7.4V it stores 74 Wh. Same mAh, double voltage, double energy.
Real-world uses for Wh conversion
- Checking if a power bank is airline-compliant
- Comparing battery backup systems
- Estimating runtime for lights, routers, cameras, and laptops
- Understanding e-bike and RC battery specifications
Nominal vs usable battery energy
Your calculated Wh is usually the nominal battery energy. In practical use, conversion losses reduce usable output. That is why this calculator includes an efficiency field. If efficiency is set to 90%, a 100 Wh pack may provide about 90 Wh of usable energy at the device output.
Frequently asked questions
Can I convert Wh back to mAh?
Yes. Rearrange the formula: mAh = (Wh × 1000) ÷ V.
What voltage should I enter for a power bank?
Use the internal cell nominal voltage when converting listed cell capacity (often 3.7V for lithium-ion). If a manufacturer provides capacity at 5V output, then use 5V.
Is bigger mAh always better?
Not always. Higher mAh can help, but Wh is the fair comparison metric across different voltages and battery types.
Bottom line
If you need a reliable battery capacity calculator, use Wh as your main metric. This mAh to Wh converter makes that quick and precise: just enter capacity, voltage, and optionally efficiency to estimate real usable power.