What Is the Wh to Ah Calculator?
This calculator converts a battery's energy rating in watt-hours (Wh) into its capacity in amp-hours (Ah). Watt-hours measure total energy, while amp-hours measure charge at a given voltage. Because the two depend on each other, you need the battery's nominal voltage to switch between them. The tool also shows the result in milliamp-hours (mAh) for smaller cells.
How to Use It
Enter the energy in watt-hours and the battery's nominal voltage. Click calculate to see the capacity in amp-hours and milliamp-hours. For a typical lead-acid or LiFePO₄ system use 12 V, 24 V, or 48 V; for a single lithium-ion cell use about 3.7 V.
The Formula Explained
The relationship is simply $$\text{Ah} = \frac{\text{Wh}}{\text{V}}$$ Energy (in watt-hours) is power multiplied by time, and power equals voltage times current. Dividing energy by voltage removes the voltage term and leaves charge over time — amp-hours. Note the result depends entirely on the voltage you choose, so always use the battery's nominal voltage.
Worked Example
A solar battery is rated at 1200 Wh and runs at 12 V. Capacity $$= 1200 \div 12 = \textbf{100 Ah},$$ equal to 100,000 mAh. If the same energy were stored at 24 V, the capacity would be only 50 Ah, since higher voltage stores the same energy with less charge.
FAQ
Why do I need voltage? Watt-hours and amp-hours are different quantities; voltage is the bridge that converts between energy and charge.
What voltage should I use? Use the battery's nominal (rated) voltage, not its fully charged peak voltage, for the most accurate everyday capacity.
Can I convert back? Yes — multiply amp-hours by voltage to return to watt-hours: \(\text{Wh} = \text{Ah} \times \text{V}\).
