About RuntimeCalculator

RuntimeCalculator is an independent tool site. It publishes calculators that estimate how long a battery can run a load, and what size battery a load needs. It is not a battery dealer. It does not sell batteries from this site, and it is not a store.

The numbers are editorial estimates from the formulas on the methodology page. They are not a measurement of your battery, not a certification, and not a wiring diagram. If a result would be dangerous to get wrong, ask an electrician and follow the equipment maker.

Some pages link to merchants. If an affiliate program is approved later, RuntimeCalculator may earn a commission. That relationship is described on the affiliate disclosure. It does not change the math. Prices, if you follow a link, are whatever the merchant shows at the time. This site does not store a price.

The calculators are the battery runtime calculator, the amp hour calculator, the UPS runtime calculator, and the battery capacity calculator.

Updated October 5, 2026