Ah to Wh calculator
Convert battery capacity to energy and back: Ah and mAh to Wh and kWh at a known system voltage, with the assumption shown.
How the Ah to Wh conversion works
Amp-hours describe electric charge, watt-hours describe energy. One cannot be turned into the other without a voltage, which is why this calculator always asks for it:
Energy (Wh) = capacity (Ah) × nominal voltage (V)
Capacity (Ah) = energy (Wh) ÷ nominal voltage (V)
Capacity (Ah) = capacity (mAh) ÷ 1000 · Energy (kWh) = energy (Wh) ÷ 1000
The result uses the nominal voltage you enter, not the voltage the battery actually holds while charging or discharging. It is a label-to-label conversion, not a measurement of stored energy: usable energy is always lower and depends on chemistry, temperature, age and discharge current.
Worked examples
100 Ah at 12 V gives 1200 Wh, that is 1.2 kWh.
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A power bank labelled 20000 mAh at a cell voltage of 3.7 V holds 20 Ah and about 74 Wh. Converting the same label at the 5 V USB output would overstate the energy by more than a third.
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2.4 kWh at 48 V corresponds to 50 Ah.
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Frequently asked questions
How do I convert Ah to Wh?
Multiply the capacity in amp-hours by the nominal voltage. 100 Ah at 12 V gives 1200 Wh. Without a voltage the conversion has no answer, because amp-hours and watt-hours measure different quantities.
How do I convert Wh to Ah?
Divide the energy in watt-hours by the nominal voltage. 1200 Wh at 12 V gives 100 Ah, while the same 1200 Wh at 24 V gives 50 Ah.
Which voltage should I use for a power bank?
Use the cell voltage, typically 3.6 to 3.7 V, because the mAh figure on the case refers to the cells. The 5 V USB output is produced by a converter and using it overstates the energy. If the manufacturer prints watt-hours, prefer that value.
Why do two batteries with the same Ah hold different energy?
Because energy also depends on voltage. A 12 V 100 Ah battery holds 1200 Wh, while a 24 V 100 Ah battery holds 2400 Wh.
Is the converted energy the energy I can actually use?
No. It is the nominal figure from the label. Usable energy is lower and depends on the permitted depth of discharge, conversion losses, temperature, age and discharge current.
Should I enter the voltage of one battery or of the whole bank?
Enter the voltage that belongs to the capacity you typed. For a series bank, both figures must describe the complete bank.
Does mAh mean the same thing as mA?
No. Milliampere-hours measure charge over time, while milliamperes measure current at a moment. A device drawing 500 mA from a 1000 mAh cell runs for roughly two hours in an ideal case.
Does the calculator work offline?
Yes, after the application has loaded once and its offline files have been cached. Nothing you type is sent anywhere.
Sources
- Nominal voltage and rated capacity of a specific product: the battery manufacturer’s label and data sheet.