Tools
Free tools
Five free, brand-neutral tools. The math is shown on each page so you can check it against your own appliance labels.
Generator size calculator
Pick the appliances you need during an outage. We add running watts, then the single largest starting surge, and show the size class that fits.
Open the tool →RV amp calculator
Check whether your RV loads fit a 30-amp or 50-amp service and how many generator watts you need to feed it.
Open the tool →Fuel run-time estimator
Use your generator’s own spec-sheet numbers to estimate hours per tank and fuel for a multi-day outage.
Open the tool →Watts, amps and volts converter
Turn a nameplate amp rating into watts (or back), with an optional power factor for motors.
Open the tool →Outage prep checklist
A tick-off checklist for before, during, and after a power outage. It saves in your browser.
Open the tool →How our tools work
Each calculator shows its formula. Appliance wattages are editable defaults taken from the upper end of published ranges, so results lean toward enough power rather than too little. Your appliance’s nameplate always wins over our defaults.
Start with the generator size calculator. Tick only what must run at the same time, replace our default wattages with the numbers on your appliance labels, and note two results: the running total with headroom and the peak when the biggest motor starts. Those are the two numbers to compare against any generator's running and starting ratings.
If a label lists amps instead of watts, use the converter first. If you are planning for an RV, the RV amp calculator checks your loads against the 30-amp or 50-amp limit. Once you know roughly what size generator you have or want, the fuel run-time estimator uses its spec-sheet run time to plan fuel for a multi-day outage, and the checklist covers the safety steps that matter most: outdoor placement, carbon monoxide alarms, and never backfeeding a house outlet.
Nothing you type into a tool is saved on our servers unless the tool says so. Letter builders and checklists run entirely in your browser.