Amp-Hours to kWh Battery Calculator

Battery capacity is often listed in amp-hours. Multiply by the battery's voltage to get its energy in watt-hours and kWh, or go the other way.

How it works

Watt-hours = amp-hours × volts. kWh = watt-hours ÷ 1,000. Amp-hours = watt-hours ÷ volts. Usable energy = energy × usable share ÷ 100; rated Ah needed = usable Ah ÷ usable share.

Worked example: DOE/NREL fact sheet example: 12 V × 100 Ah = 1,200 Wh = 1.2 kWh. In reverse, 1 kWh at 24 V = 1,000 ÷ 24 = 41.7 Ah.

Assumptions

Uses the battery's nominal voltage. Real voltage changes as a battery discharges.
Amp-hour ratings are given at a specified discharge rate and temperature. The DOE lead-acid battery handbook notes capacity varies with the discharge rate: the higher the discharge rate, the lower the capacity.
The usable share defaults to 100%. Many batteries should not be fully discharged (the DOE/NREL fact sheet notes this for lead-acid batteries), so set your own usable share.
For a pack, enter the pack's total nominal voltage and total amp-hours. Conversion losses in inverters or chargers are not included.

Frequently asked questions

How many kWh is a 12V 100Ah battery?

12 V × 100 Ah = 1,200 Wh = 1.2 kWh. This is the example used in a U.S. DOE/NREL fact sheet, which notes it equals a 2 V, 600 Ah battery.

How many amp-hours do I need for 1 kWh at 24 volts?

1,000 Wh ÷ 24 V = 41.7 Ah of usable storage (the DOE/NREL fact sheet rounds this to 42 Ah). You need more rated capacity if you cannot use all of it.

Why might I get less energy than the rating?

Capacity depends on how fast the battery is discharged and on temperature. The DOE handbook explains that higher discharge rates give lower capacity, and ratings are usually stated at 25°C (77°F).

Related calculators

Sources

Formulas and reference values are from these sources. Page last reviewed 2026-10-19.