BackupCalc is an independent website with free calculators for backup power. It helps people answer practical questions before a power cut, or before they buy: how long will a power station run my fridge? Can it start my sump pump? How many solar panels do I need to keep it charged?
Who's behind BackupCalc
Hi, I'm Anuj, a developer. I built BackupCalc because simple questions about backup power turned out to be surprisingly hard to answer. Most of what I found was written by the brands selling the batteries, and their numbers often disagreed with each other.
So every calculator here uses one open method, explained step by step, and every power station spec is checked against the manufacturer's own pages. If a result doesn't match what you see with your own equipment, I'd like to hear about it.
What we do differently
- No signup, no sales calls. Every calculator works instantly in your browser. We never ask for your email, phone number or ZIP code to show a result.
- The math is shown. Each tool explains its formula and assumptions, so you can check our work. See how we calculate runtime.
- Realistic numbers. We use average watts for appliances that cycle, real-world efficiency losses and startup surge checks, rather than best-case figures.
- Maintained data. Appliance and power station figures are reviewed regularly. Last review: 2026-10-26.
Corrections
If you spot a wrong number, an outdated spec or a calculation that doesn't match your own measurements, please tell us. Real-world measurements from readers are the best way to improve the data.
Important
Our results are estimates for planning. Always follow your equipment's manuals, and use a licensed electrician for anything connected to your home's wiring. See our terms and disclaimer.