Wh = Ah x V. For milliamp hours, use Wh = mAh x V / 1000. This is the formula to convert amp hours to watt hours for battery sizing.
Ah stands for amp hours, a measure of electric charge. V is the nominal voltage of the battery, in volts. Wh is watt hours, a measure of stored energy. For mAh (milliamp hours), divide by 1000 to get Ah before multiplying by voltage.
How do I convert amp hours to watt hours for real batteries?
Use the battery’s nominal voltage in the formula. The table below shows common conversions for battery sizes and voltages found in actual specifications.
| Capacity (Ah) | Voltage (V) | Energy (Wh) |
|---|---|---|
| 5 | 12.8 | 64 |
| 10 | 12.8 | 128 |
| 50 | 12.8 | 640 |
| 100 | 12.8 | 1280 |
| 100 | 51.2 | 5120 |
| 200 | 51.2 | 10240 |
| 280 | 384 | 107520 |
| 37 | 409.6 | 15155 |
What are worked examples for amp hour to watt hour conversion?
Example 1: A 12V battery rated at 100Ah. Wh = 100 x 12 = 1200Wh.
Example 2: A 51.2V battery rated at 200Ah. Wh = 200 x 51.2 = 10240Wh.
Example 3: A 280Ah battery at 384V. Wh = 280 x 384 = 107520Wh.
What is the most common mistake in amp hour to watt hour conversion?
The most common mistake is confusing mAh with Ah or using the wrong voltage. For example, 10,000mAh is 10Ah, not 10,000Ah. Always use the nominal voltage, not maximum or minimum, for sizing. Using the wrong unit or voltage can result in undersized or oversized systems.
Why does amp hours to watt hours conversion matter in procurement?
Procurement decisions compare batteries on usable energy, not just charge. Watt hours (Wh) account for both capacity and voltage, allowing direct comparison across different battery chemistries and configurations. Suppliers quote in Wh or kWh for this reason.
How do I apply the formula to my own battery specification?
Find the rated amp hours and nominal voltage on the battery label or datasheet. Multiply them to get watt hours. For mAh, divide by 1000 first. If the battery is rated at 100Ah and 51.2V, Wh = 100 x 51.2 = 5120Wh.
Check your battery specification and run the calculation with your actual values before ordering or quoting.
Frequently asked questions
Can I use maximum voltage instead of nominal voltage for amp hour to watt hour conversion?
No. Always use the nominal voltage stated in the battery specification. Maximum voltage overstates the energy and leads to sizing errors.
How do I convert mAh to Wh for small batteries?
Use Wh = mAh x V / 1000. For example, a 2000mAh (2Ah) 3.7V cell gives Wh = 2000 x 3.7 / 1000 = 7.4Wh.
Why do some batteries list only Ah and not Wh?
Some legacy or low-voltage batteries list only Ah. To compare energy content, you must multiply by the nominal voltage to get Wh.
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