Watt-Hours Calculator: Convert Ah and Volts to Wh

Amp-hours alone do not tell you how much energy a battery holds, because energy also depends on voltage. A 100 Ah battery at 12 V stores half the energy of a 100 Ah battery at 24 V, even though the amp-hour number is identical. Watt-hours combine charge and voltage into a single energy figure, which is what your loads consume and what solar sizing is based on. Converting to watt-hours lets you compare batteries of different voltages fairly and plan how long they will last.

Multiply the nominal watt-hours by the depth of discharge you can safely use. A 1,200 Wh lead-acid battery at 50 percent gives about 600 usable watt-hours, while a 1,200 Wh lithium battery at 80 percent gives about 960. This calculator shows nominal energy; for planning, apply your chemistry depth of discharge to get the figure that actually covers your loads. Inverter and wiring losses then trim a little more off what reaches your devices.

They measure the same thing at different scales: a kilowatt-hour is simply 1,000 watt-hours. Small batteries and individual devices are usually described in watt-hours, while home energy bills and larger battery banks use kilowatt-hours. To convert, divide watt-hours by 1,000 to get kilowatt-hours, or multiply the other way. A 1,200 Wh battery is 1.2 kWh, and a 5 kWh home battery is 5,000 Wh.

Divide the usable watt-hours by the device power in watts. A 1,200 Wh battery at 80 percent usable, about 960 Wh, running a 100 W load lasts roughly 9.6 hours before recharge, minus inverter losses. Higher loads drain it faster in direct proportion. For a dedicated runtime estimate that also accounts for depth of discharge, use the battery runtime calculator, which performs this division for you.

Yes. Cold reduces the capacity you can actually withdraw, particularly from lead-acid batteries, where freezing temperatures can cut available energy substantially. Lithium handles cold better for discharge but should not be charged below freezing without a heater or protection circuit. The amp-hour rating on the label is given at a standard temperature, usually around 25 degrees Celsius, so plan for less in cold conditions and keep batteries insulated where possible.