Wh = Ah x V is the formula to convert amp hours to watt hours for battery sizing.
In this formula, Wh stands for watt hours, Ah for amp hours, and V for voltage. All values must use the same time base (typically hours) and the nominal voltage of the battery.
| Capacity (Ah) | Voltage (V) | Energy (Wh) |
|---|---|---|
| 5 | 12.8 | 64 |
| 10 | 12.8 | 128 |
| 50 | 12.8 | 640 |
| 100 | 12.8 | 1,280 |
| 100 | 51.2 | 5,120 |
| 200 | 51.2 | 10,240 |
| 280 | 384 | 107,520 |
| 600 | 51.2 | 30,720 |
How do you convert amp hours to watt hours?
To convert amp hours to watt hours, multiply the amp hour (Ah) rating by the nominal voltage (V) of the battery: Wh = Ah x V. For example, a 100Ah battery at 12.8V gives 1,280Wh (100 x 12.8 = 1,280Wh).
What are some worked examples of amp hour to watt hour conversion?
Example 1: A 200Ah battery at 51.2V. Calculation: 200 x 51.2 = 10,240Wh.
Example 2: A 280Ah battery at 384V. Calculation: 280 x 384 = 107,520Wh.
Example 3: A 100Ah battery at 12.8V. Calculation: 100 x 12.8 = 1,280Wh.
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). 1Ah = 1,000mAh, so using the wrong unit results in a 1,000-fold error. Another error is using peak or charging voltage instead of the nominal voltage, which overstates the energy capacity. Always confirm the voltage used in the supplier’s datasheet and clarify if the stated capacity is nominal or maximum.
Why does amp hour to watt hour conversion matter in procurement?
Procurement decisions based on amp hours alone ignore the impact of voltage on total energy. Two batteries with the same Ah but different voltages deliver different Wh, affecting runtime and system design. Freight classification, certification scope, and cost per Wh all depend on the correct Wh figure, not just Ah. Always request both Ah and nominal voltage for every battery quoted.
What should a buyer verify before accepting a supplier’s amp hour to watt hour calculation?
Request the supplier’s datasheet and ask: “What nominal voltage is used for your Wh calculation? Is the Ah rating based on the IEC 62619 standard, and what is the depth of discharge assumed?” This ensures the quoted Wh is comparable across suppliers and relevant for your application.
Next action: Check your battery specification for both Ah and nominal voltage, then run the calculation to confirm the Wh figure matches the supplier’s claim.
Frequently asked questions
Can I use mAh instead of Ah in the amp hours to watt hours formula?
Yes, but you must convert mAh to Ah first by dividing by 1,000. For example, 5,000mAh = 5Ah. Then use Wh = Ah x V.
Does the amp hours to watt hours formula account for depth of discharge?
No, Wh = Ah x V gives the theoretical total energy. Usable energy depends on the depth of discharge (DoD), which should be specified separately.
Why do some batteries with the same Ah rating have different Wh ratings?
Because Wh depends on both Ah and voltage. Higher voltage batteries with the same Ah provide more energy in Wh.
AJPOWER-Battery