Wh = Ah x V is the formula for converting amp hours to watt hours for battery sizing.
In this formula, Wh stands for watt hours, Ah for amp hours, and V for the battery’s nominal voltage in volts. Always use the rated amp hour value (not milliamp hours) and the nominal voltage as listed in the battery specification.
How do you convert amp hours to watt hours?
To convert amp hours (Ah) to watt hours (Wh), multiply the amp hour value by the battery’s nominal voltage. For example, a 100Ah battery at 12V provides 1,200Wh of energy (100 x 12 = 1,200).
| Amp Hours (Ah) | Nominal Voltage (V) | Watt Hours (Wh) |
|---|---|---|
| 50 | 12 | 600 |
| 100 | 12 | 1,200 |
| 200 | 12 | 2,400 |
| 100 | 24 | 2,400 |
| 200 | 24 | 4,800 |
| 100 | 48 | 4,800 |
| 200 | 48 | 9,600 |
| 280 | 384 | 107,520 |
What are worked examples for amp hour to watt hour conversion?
Example 1: A 24V battery rated at 100Ah: 100 x 24 = 2,400Wh.
Example 2: A 48V battery rated at 200Ah: 200 x 48 = 9,600Wh.
Example 3: A 384V battery rated at 280Ah: 280 x 384 = 107,520Wh.
What is the most common mistake when converting amp hours to watt hours?
The most common mistake is using the wrong voltage or confusing amp hours (Ah) with milliamp hours (mAh). Always check that the amp hour value matches the voltage used in the calculation, and do not use mAh unless you convert it to Ah first (1,000mAh = 1Ah). Another frequent error is assuming all of the rated capacity is usable—depth of discharge limits may reduce actual usable watt hours.
Why does amp hour to watt hour conversion matter in procurement?
Accurate conversion from amp hours to watt hours is essential for comparing battery energy capacities across suppliers. Quoting only amp hours without voltage leads to mismatched energy figures and procurement risk. Careful buyers always request both amp hour and nominal voltage values, and verify that suppliers use the same measurement conditions.
What should you ask a supplier to verify amp hour and watt hour ratings?
Ask the supplier: “Please confirm the nominal voltage and rated amp hour capacity for each battery, and provide the calculated watt hour value based on these figures. State the test conditions used for these ratings.”
Before signing, run the amp hours to watt hours calculation using the supplier’s figures to confirm the quoted energy capacity matches your requirements.
Frequently asked questions
Can I use amp hours alone to compare battery energy?
No, amp hours (Ah) alone do not indicate total energy. You must multiply by the battery's nominal voltage to get watt hours (Wh), which reflects actual stored energy.
What if the battery is rated in milliamp hours (mAh)?
Convert milliamp hours (mAh) to amp hours (Ah) by dividing by 1,000. Then use the formula: Wh = Ah x V. For example, 10,000mAh = 10Ah.
Does depth of discharge affect the usable watt hours?
Yes, most batteries are not used at 100% depth of discharge (DoD). For example, a 5.12kWh battery at 80% DoD provides 4.1kWh usable energy. Always ask for usable Wh at specified DoD.
AJPOWER-Battery