Watt Hour Calculator

Multiply the voltage by the amp-hours. A 12 volt battery rated 100 Ah holds 12 times 100, which is 1200 watt-hours. The tool does this the moment both fields are filled.

Multiply the power in watts by the time in hours. A 60 watt device running 5 hours uses 60 times 5, which is 300 watt-hours. Switch to the watts and hours mode to enter these two figures.

Milliamp-hours measure charge at a given voltage, while watt-hours measure energy. Two packs can share a mAh rating yet hold very different energy if their voltages differ, so watt-hours are the fairer way to compare them.

Milliamp-hours depend on voltage, and the watts and hours inputs never state one. The tool shows milliamp-hours only in the volts and amp-hours mode, where the voltage is known, and displays n/a otherwise.

Divide watt-hours by 1000. So 1200 watt-hours is 1.2 kilowatt-hours, the unit your electricity bill charges by. The tool prints both figures side by side.

Yes, with a quick two-step. Work out the battery energy in watt-hours here, then divide by the device wattage to get rough hours. A 1200 Wh battery driving a 100 W load lasts about 12 hours before real-world losses.

Yes. Every field accepts decimals, so a 3.7 volt cell rated 2.6 Ah reads as 9.62 watt-hours. Watt-hours are rounded to four decimal places and kilowatt-hours to six, which keeps tiny values readable.

Both values in the active mode must be positive numbers. A blank, zero or negative entry shows a short prompt instead of a result, since energy cannot be computed from an incomplete pair.

No. The arithmetic runs entirely in your browser, so the ratings you type never leave your device and there is nothing to upload or store.