Wh = Ah x V is the formula to convert amp hours to watt hours for battery sizing in procurement and technical evaluation.
In this formula, Wh stands for watt hours, Ah for amp hours, and V for the nominal voltage of the battery. If the battery capacity is given in milliamp hours (mAh), use Wh = mAh x V / 1000 to convert to watt hours.
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 battery’s nominal voltage (V). For milliamp hours (mAh), first divide by 1000 to get Ah, then multiply by voltage. The table below shows conversions for common battery ratings:
| Capacity (Ah) | Voltage (V) | Capacity (mAh) | Watt Hours (Wh) |
|---|---|---|---|
| 1 | 3.2 | 1000 | 3.2 |
| 2.5 | 12.8 | 2500 | 32 |
| 10 | 12.8 | 10000 | 128 |
| 50 | 51.2 | 50000 | 2560 |
| 100 | 51.2 | 100000 | 5120 |
| 200 | 51.2 | 200000 | 10240 |
| 280 | 384 | 280000 | 107520 |
| 600 | 51.2 | 600000 | 30720 |
What are worked examples of 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 10,000mAh (10Ah) 3.7V cell: Wh = 10 x 3.7 = 37Wh.
What mistakes do buyers make when converting amp hours to watt hours?
The most common mistake is confusing mAh (milliamp hours) with Ah (amp hours), leading to a 1000x error. Another frequent error is using the wrong voltage—always use the battery’s nominal voltage, not the charger or system voltage. Buyers sometimes assume the full rated capacity is usable, ignoring depth-of-discharge limits specified in technical data sheets.
Why does amp hour to watt hour conversion matter in procurement?
Accurate conversion ensures you compare batteries on usable energy, not just capacity. Suppliers may quote amp hours at different voltages, making direct comparison misleading. Always request both amp hour and nominal voltage ratings, and convert to watt hours for fair evaluation. Ask suppliers: “Please confirm the nominal voltage used for the amp hour rating and provide the watt hour value for each model.”
What should I verify before finalizing a battery order?
Check that the amp hour and voltage ratings are clearly stated and match the technical data sheet. Confirm whether the quoted capacity is total or usable (after depth-of-discharge limits). For shipments, clarify if the watt hour value aligns with UN 38.3 or IEC 62619 certification documents, as these affect transport and compliance risks.
Next action: Run the amp hours to watt hours calculation on your shortlisted battery models and request the supplier’s technical data sheet to confirm the figures.
Frequently asked questions
Can I use amp hour to watt hour conversion for any battery chemistry?
Yes, the formula Wh = Ah x V applies to all battery chemistries, but always use the nominal voltage specific to the chemistry (e.g., 3.2V for LiFePO4, 3.7V for standard lithium-ion).
Why do some datasheets list only amp hours or only watt hours?
Some suppliers highlight amp hours to make capacity look larger, but watt hours reflect actual energy. Always request both values and the nominal voltage for accurate comparison.
How does depth of discharge affect usable watt hours?
Usable watt hours are lower than rated watt hours if depth-of-discharge (DoD) is limited. For example, if a 5kWh battery is rated for 80% DoD, only 4kWh is usable per cycle.
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