Wh = Ah x V. To convert amp hours to watt hours, multiply the battery capacity in amp hours (Ah) by the nominal voltage (V) of the battery.
Ah stands for amp hours, the total charge a battery can deliver over one hour. V is the nominal voltage in volts. Wh is watt hours, the total energy stored. For milliamp hours (mAh), use Wh = mAh x V / 1000 to convert to watt hours.
| Capacity (Ah) | Voltage (V) | Energy (Wh) |
|---|---|---|
| 1 | 3.2 | 3.2 |
| 2.5 | 12.8 | 32 |
| 5 | 12.8 | 64 |
| 10 | 12.8 | 128 |
| 50 | 51.2 | 2,560 |
| 100 | 51.2 | 5,120 |
| 200 | 51.2 | 10,240 |
| 280 | 384 | 107,520 |
How do you convert amp hours to watt hours for battery sizing?
Multiply the amp hour (Ah) rating by the nominal voltage (V) to get watt hours (Wh). For example, a 100Ah battery at 51.2V: 100 x 51.2 = 5,120Wh. For milliamp hours (mAh), divide by 1,000: 2,600mAh at 3.7V is 2.6 x 3.7 = 9.62Wh.
What are some worked examples for common battery specifications?
Example 1: A 12V, 100Ah battery. 100 x 12 = 1,200Wh.
Example 2: A 51.2V, 200Ah battery. 200 x 51.2 = 10,240Wh.
Example 3: A 3.2V, 50Ah cell. 50 x 3.2 = 160Wh.
What is the most common mistake in amp hour to watt hour conversion?
The most common mistake is confusing mAh with Ah. 1,000mAh = 1Ah. Always use amp hours (Ah) in the formula. Another error is using the wrong voltage—use the battery’s nominal voltage, not the system or charger voltage. Mixing up these units leads to incorrect sizing.
Why does the amp hours to watt hours figure matter in procurement?
Watt hours (Wh) determine the total energy a battery can deliver. Procurement decisions depend on matching the required Wh to the application’s load and runtime. Always check if the quoted Wh is total or usable (after depth-of-discharge limits). For example, a 5,120Wh battery at 80% DoD provides 4,096Wh usable energy.
What should you do next?
Check your battery’s datasheet for Ah and nominal voltage, then run the calculation to confirm the watt hour rating matches your application’s requirements.
Frequently asked questions
How do you convert 2,600mAh at 3.7V to watt hours?
2,600mAh is 2.6Ah. Multiply by 3.7V: 2.6 x 3.7 = 9.62Wh.
Does depth of discharge affect amp hour to watt hour conversion?
No, the formula gives total Wh. Usable Wh is lower after applying the depth-of-discharge limit (e.g., 80% DoD).
Is it correct to use peak or charging voltage for this calculation?
No, always use the nominal voltage of the battery for amp hour to watt hour conversion.
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