Tools

Free tools that do the power math for you. The power station calculator adds up the devices you want to run, tells you how many watt-hours and watts you need, and shows how long a given battery would last. It uses the same formula and assumptions as every article on this site: about 85% of rated capacity is usable, plus roughly 10 W for the inverter with small AC loads.

Prefer to do it by hand? Follow our 4-step sizing guide, or see How We Research for the full list of assumptions. Want a printable version? Subscribe below the calculator and we’ll email you our free Power Outage Runtime Chart.