Size your backup power with real math, not a sales pitch.
Generator, portable power station, or home battery: find out how much you actually need for the things that matter in an outage. The math is shown, every number is editable, and it's checked by a practicing power-electronics engineer.
How it works
- Pick your essentials. Fridge, furnace blower, sump or well pump, lights, CPAP. Use your own nameplate watts if you have them.
- Set your outage. Hours without power, fuel type, and elevation. We derate for propane, natural gas and altitude.
- Get honest numbers. Running watts, starting surge, and kWh, with the formulas shown. Often you need less than you were told.
- Never backfeed a generator by plugging it into a wall outlet. It can electrocute utility line workers and neighbors and bypasses your home's protection (CPSC).
- Connecting any generator or battery to house wiring requires a transfer switch or listed interlock installed by a licensed electrician, with permits where your city or county requires them.
- Carbon monoxide kills. Run portable generators outside only, at least 20 feet from the house, exhaust pointed away, never in a garage, basement, shed or porch. Install battery-backed CO alarms (CPSC).
- This tool gives general estimates, not electrical design or professional advice. Follow your equipment manuals and local code. Full safety notes & disclaimer.
Why trust these numbers?
Show-the-math
Every result explains how it was calculated, and every default comes with a cited source.
Brand-neutral
The calculator recommends sizes, not brands. Any paid link is labeled right next to it.
Built for the Plains
Kansas outage data, winter furnace loads, well pumps and storm-season realities.
Start with a guide
How to Size a Home Generator Without Overpaying
How to size a home generator without overpaying: running watts, starting watts, fuel and altitude derates, explained by an engineer.
Portable Power Station vs. Generator vs. Whole-Home Battery: What Makes Sense for Kansas Outages
Portable power station, generator, or home battery? A plain comparison using real Kansas outage data from the EIA.
Running Watts vs. Starting Watts, and Why Your Furnace and Well Pump Matter
Running watts vs. starting watts, and why your furnace blower and well pump decide what size backup you need.