To convert amp hours to watt hours, use the formula: Wh = Ah x V.
In this formula, Wh stands for watt hours, Ah is amp hours, and V is the nominal voltage of the battery. Always use amp hours (Ah), not milliamp hours (mAh), for this calculation unless you convert mAh to Ah first (1 Ah = 1,000 mAh).
How do I use the amp hours to watt hours formula?
Multiply the battery’s amp hour rating by its nominal voltage. For example, a 100Ah battery at 12.8V gives Wh = 100 x 12.8 = 1,280Wh. This tells you the total energy the battery can deliver if fully discharged.
| Amp Hours (Ah) | Nominal Voltage (V) | Watt Hours (Wh) |
|---|---|---|
| 50 | 12.8 | 640 |
| 100 | 12.8 | 1,280 |
| 200 | 12.8 | 2,560 |
| 100 | 51.2 | 5,120 |
| 200 | 51.2 | 10,240 |
| 280 | 384 | 107,520 |
| 460 | 51.2 | 23,552 |
| 600 | 51.2 | 30,720 |
What are some worked examples for amp hour to watt hour conversion?
Example 1: A 200Ah battery at 12.8V: Wh = 200 x 12.8 = 2,560Wh.
Example 2: A 100Ah battery at 51.2V: Wh = 100 x 51.2 = 5,120Wh.
Example 3: A 280Ah battery at 384V: Wh = 280 x 384 = 107,520Wh.
What mistakes do buyers make when converting amp hours to watt hours?
The most common mistake is using the wrong voltage—either rounding to 12V instead of using 12.8V, or not checking if the battery is 48V, 51.2V, or another value. Another frequent error is confusing amp hours (Ah) with milliamp hours (mAh), which leads to a result off by a factor of 1,000. Finally, buyers sometimes forget that the rated capacity is not always the usable capacity. Depth-of-discharge limits (like 80% DoD) mean you can only use part of the total watt hour figure in practice.
Why does the amp hours to watt hours figure matter in battery procurement?
Suppliers quote battery capacity in amp hours, watt hours, or kilowatt hours. If you compare batteries only by Ah, you might miss that a higher voltage battery stores more energy for the same Ah rating. For accurate sizing, always convert to Wh or kWh using the actual nominal voltage. This ensures you match your load requirements and avoid undersizing or overspending.
How do I check a battery spec sheet for the right values?
Look for the nominal voltage and rated amp hours on the specification sheet. Ignore marketing claims about peak or surge capacity. For example, AJPOWER lists both values clearly for each model. If you see only Ah, ask the supplier for the nominal voltage before calculating Wh.
Next, check your battery spec sheet for nominal voltage and amp hours, then run the calculation for your own application.
Frequently asked questions
Can I use the same formula for lithium, lead-acid, and other battery types?
Yes, the formula Wh = Ah x V applies to all battery chemistries, but always use the correct nominal voltage for the specific battery type.
What if my battery is rated in mAh instead of Ah?
Divide the mAh value by 1,000 to get Ah, then use the formula. For example, 5,000mAh is 5Ah, so Wh = 5 x V.
Does depth of discharge affect the amp hour to watt hour calculation?
The formula gives total theoretical capacity. Usable energy is lower due to depth-of-discharge limits (e.g., 80% DoD), so multiply Wh by the usable percentage for real-world sizing.
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