// Free calculators

Backup power tools

Six calculators that answer the questions people actually ask before buying a generator. They run entirely in your browser, so the numbers you type stay on your device.

⚡ Sizing
Generator Sizing Calculator

Pick the appliances you need during an outage and get the running watts, the largest starting surge and the generator size that covers both.

⛽ Runtime & fuel
Runtime & Fuel Cost Calculator

Estimate hours per tank, gallons per hour and what a three-day outage costs on gasoline, propane, diesel or natural gas.

🔀 Transfer switch
Transfer Switch Planner

Choose the circuits you want backed up and see the switch type, circuit count and inlet amperage to ask an electrician for.

🔌 Cord gauge
Extension Cord Gauge Calculator

Find the wire gauge a generator cord run actually needs, based on load, distance and acceptable voltage drop.

🔋 Battery sizing
Battery Backup & Solar Sizing

Convert your load list into watt-hours, size a battery power station and see how long solar takes to refill it.

✅ Readiness
Outage Readiness Checklist

A 30-point interactive checklist covering equipment, fuel, water, medical needs and the day-three failures. Progress saves in your browser.