Backup power planning

Generator Runtime Estimator

Use your generator’s manufacturer fuel-use table and a realistic essential-load list to plan runtime and reserve fuel.

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Carbon-monoxide safety: generators stay outdoors only

CDC says to operate a generator outdoors, more than 20 feet from windows, doors, and vents. Never use one in a home, garage, basement, or shed. Use working battery or battery-backup carbon-monoxide alarms and follow the exact manual. Read CDC carbon-monoxide guidance.

Estimate runtime from your manual

Enter the fuel-use figures printed for your generator at 25%, 50%, and 75% load. This tool does not substitute a generic fuel-burn formula.

Fuel and generator rating

GasolineDieselPropane (liquid gallons)

Available fuel

Fuel available for this outage, in liquid gallons.

Rated running watts

Use the running-watts rating, not starting/surge watts.

Essential loads

The calculator remains within the 25-75% manufacturer data band. Reduce loads if your selected essentials exceed 75% of rated running watts.

Refrigerator150 W running loadLED lights60 W running loadInternet / phone charging45 W running loadMedical device120 W running loadSump pump800 W running load

Custom load watts

Optional running watts not listed above.

Manufacturer fuel-use figures

Copy these values from the manufacturer manual for the exact generator and fuel type. Units are gallons per hour.

At 25% load

At 50% load

At 75% load

Use the result well

Plan runtime without guessing at fuel use

Use the exact figures from your generator manual, keep the planned electrical load comfortably below the rated output, and protect a reserve for changing conditions.

Step 1
Copy the model's fuel-use figures and units from its manual, then enter the fuel you can safely store and rotate.
Step 2
Add essential running loads, check startup requirements separately, and keep the plan at or below 75 percent of rated output.
Step 3
Plan a reserve, review refueling and carbon-monoxide safety, and test the equipment outdoors before an emergency.

Questions about this estimate

Why do I need the manufacturer fuel-use table?

Fuel consumption varies by model, fuel, load, maintenance, temperature, and altitude. The model-specific manual is more dependable than a generic gallons-per-hour assumption.

Can I enter propane in pounds instead of gallons?

Use one consistent liquid-volume unit for both available fuel and the manual's consumption rate. Do not mix pounds, gallons, liters, or gaseous-volume figures without a verified conversion for the exact fuel conditions.

Where is it safe to run a portable generator?

Run it outdoors and follow the manual plus current CPSC and CDC guidance. Keep it away from doors, windows, and vents, never use it in a home or garage, and use working carbon-monoxide alarms.