The formula to convert amp hours to watt hours is: Wh = Ah x V.
In this formula, Wh stands for watt hours (energy), Ah stands for amp hours (capacity), and V is the nominal voltage of the battery. For milliamp hours (mAh), divide by 1,000 to get Ah before using the formula. Always use the nominal voltage listed in the battery specification, not the charging or peak voltage.
How do I convert amp hours to watt hours for real battery specifications?
To convert amp hours (Ah) to watt hours (Wh), multiply the amp hour rating by the nominal voltage of the battery. The table below shows common conversions for battery sizes and voltages found in industrial and commercial applications.
| Amp Hours (Ah) | Nominal Voltage (V) | Watt Hours (Wh) |
|---|---|---|
| 10 | 12.8 | 128 |
| 50 | 12.8 | 640 |
| 100 | 12.8 | 1,280 |
| 100 | 51.2 | 5,120 |
| 200 | 12.8 | 2,560 |
| 200 | 51.2 | 10,240 |
| 280 | 384 | 107,520 |
| 600 | 51.2 | 30,720 |
What are some worked examples of amp hour to watt hour conversion?
Example 1: A 12V 100Ah battery: Wh = 100 x 12 = 1,200 Wh.
Example 2: A 51.2V 200Ah battery: Wh = 200 x 51.2 = 10,240 Wh.
Example 3: A 384V 280Ah battery: Wh = 280 x 384 = 107,520 Wh.
What is the most common mistake when converting amp hours to watt hours?
The most common mistake is using the wrong voltage—such as the charging voltage instead of the nominal voltage—or confusing amp hours (Ah) with milliamp hours (mAh). Using the wrong voltage can misstate the usable energy by 10-20%, which may result in under- or over-sizing the battery system. Always check the specification sheet for the correct nominal voltage and ensure you are working in the right units.
Why does amp hour to watt hour conversion matter in procurement?
Accurate conversion from amp hours to watt hours is essential for comparing battery options, calculating total system energy, and ensuring compliance with project requirements. Overestimating capacity can inflate procurement costs, while underestimating can lead to system failures or warranty disputes. Buyers should always verify the conversion using the actual battery specification to avoid costly mistakes.
What should I do next to avoid conversion errors?
Check the nominal voltage and amp hour rating on your battery specification sheet and run the Wh = Ah x V calculation before finalizing your order or technical report.
Frequently asked questions
Can I use the charging voltage instead of nominal voltage for amp hour to watt hour conversion?
No, always use the nominal voltage listed in the battery specification. Using the charging or peak voltage will overstate the actual energy available and can lead to system sizing errors.
How do I convert milliamp hours (mAh) to watt hours (Wh)?
First, divide the mAh value by 1,000 to get Ah, then multiply by the nominal voltage: Wh = (mAh / 1,000) x V.
Does depth of discharge (DoD) affect amp hour to watt hour conversion?
The formula gives total rated energy. To find usable energy, multiply Wh by the DoD percentage (e.g., 80% DoD: usable Wh = Wh x 0.8).
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