Wh = mAh x V / 1000 is the formula to convert milliamp-hours (mAh) to watt-hours (Wh) for any battery or cell.
In this formula, Wh stands for watt-hours (the energy delivered), mAh is milliamp-hours (the charge capacity), and V is the nominal voltage of the battery or cell. Divide by 1000 to account for converting milliamps to amps.
What is the conversion table for mAh to Wh at common voltages?
The table below shows mAh to Wh conversions for typical lithium battery voltages (3.2V, 3.7V, 12.8V, 51.2V) and a range of capacities found in real battery specifications. Find your battery’s nominal voltage and capacity to read across for the Wh value.
| mAh | 3.2V (Wh) | 3.7V (Wh) | 12.8V (Wh) | 51.2V (Wh) |
|---|---|---|---|---|
| 1000 | 3.2 | 3.7 | 12.8 | 51.2 |
| 2000 | 6.4 | 7.4 | 25.6 | 102.4 |
| 5000 | 16.0 | 18.5 | 64.0 | 256.0 |
| 10000 | 32.0 | 37.0 | 128.0 | 512.0 |
| 20000 | 64.0 | 74.0 | 256.0 | 1024.0 |
| 50000 | 160.0 | 185.0 | 640.0 | 2560.0 |
| 100000 | 320.0 | 370.0 | 1280.0 | 5120.0 |
| 200000 | 640.0 | 740.0 | 2560.0 | 10240.0 |
How do you use the mAh to Wh formula with real battery data?
Example 1: A 12V 100Ah battery. First, convert 100Ah to mAh: 100Ah x 1000 = 100,000mAh. Wh = 100,000 x 12 / 1000 = 1,200Wh.
Example 2: A 3.2V cell rated at 5,000mAh. Wh = 5,000 x 3.2 / 1000 = 16Wh.
Example 3: A 51.2V battery with 200Ah. 200Ah x 1000 = 200,000mAh. Wh = 200,000 x 51.2 / 1000 = 10,240Wh.
What is the most common mistake in mAh to Wh conversion?
The most common mistake is using amp-hours (Ah) instead of milliamp-hours (mAh), or using the wrong voltage. For example, 10,000mAh at 3.2V is 32Wh, but at 12.8V it is 128Wh. Using the wrong voltage can mean undersizing or oversizing a battery bank, which can cost thousands in procurement or lead to system failure. Always check the nominal voltage on the battery’s datasheet, not a generic value.
Why does the Wh figure matter for battery procurement?
Wh (watt-hours) is the figure that determines how much usable energy a battery can store and deliver. Procurement decisions, system sizing, and cost-per-cycle calculations all use Wh, not mAh, because Wh accounts for both capacity and voltage. If you compare batteries by mAh alone, you risk buying a system that cannot meet your load or is oversized for your budget.
How does depth of discharge affect usable Wh?
Not all of a battery’s rated Wh is usable. Depth of discharge (DoD) limits, set by chemistry or BMS, mean only a percentage of the rated Wh can be safely drawn. For example, a 10kWh battery at 80% DoD delivers 8kWh usable. Always confirm the usable Wh for your application, not just the rated figure.
Check your battery’s datasheet for nominal voltage and capacity, then run the calculation above to verify the Wh figure before specifying or ordering.
Frequently asked questions
Can I use the same mAh to Wh formula for any battery chemistry?
Yes, the formula Wh = mAh x V / 1000 applies to any battery chemistry, as long as you use the correct nominal voltage for that cell or pack.
How do I convert Wh back to mAh?
To convert Wh to mAh, use the formula: mAh = Wh x 1000 / V. Always use the battery’s nominal voltage for accurate results.
Why do battery datasheets sometimes list only Ah or mAh, not Wh?
Manufacturers may list only Ah or mAh because voltage can vary by application. Calculating Wh requires knowing the nominal voltage, which is application-specific.
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