Generator Fuel Consumption Calculator
Calculate fuel usage, cost, and runtime for your generator
Rated output of your generator in kilowatts
Type of fuel your generator uses
Percentage of generator capacity being used
Elevation above sea level (derates output above 1,000 ft)
Outside temperature (derates output above 104°F)
Results
Fuel Consumption Rate
0.21gal/hr
Fuel used per hour at this load
Daily Fuel Use (24 hr)
5.0gal/day
Total fuel for 24 hours of continuous runtime
Cost Per Day
$17.43
Estimated fuel cost for 24 hours
Runtime Per 5-gal gas can
24.1hours
Hours from one 5-gal gas can
Effective Output
5.0kW
Derated output after altitude/temperature
Efficiency Rating
50%
Good
Generator Fuel Consumption Table
Fuel consumption at sea level and 77°F. Rates vary with altitude and temperature.
| Generator | Fuel | 25% Load | 50% Load | 75% Load | 100% Load |
|---|---|---|---|---|---|
| 2 kW | Gasoline | 0.18 gal/hr | 0.17 gal/hr | 0.15 gal/hr | 0.17 gal/hr |
| 5 kW | Gasoline | 0.45 gal/hr | 0.42 gal/hr | 0.38 gal/hr | 0.42 gal/hr |
| 10 kW | Propane | 0.80 gal/hr | 0.73 gal/hr | 0.66 gal/hr | 0.73 gal/hr |
| 20 kW | Diesel | 1.36 gal/hr | 1.26 gal/hr | 1.16 gal/hr | 1.26 gal/hr |
Fuel Rate = Generator kW × Load % × SFC (gal/kWh)
Run your generator at 71-85% load for the best fuel efficiency. Below 40% load you waste fuel; above 90% you stress the engine and shorten its lifespan. Size your generator so your typical load falls in the sweet spot.
At elevations above 1,000 ft, generators lose ~3% output per 1,000 ft. A 5 kW generator at 5,000 ft only produces about 4.4 kW. Factor this in when sizing a generator for mountain or high-altitude use.
Frequently Asked Questions
What load percentage is most fuel-efficient?
The 71-85% load range is the sweet spot for fuel efficiency. Running too light (below 40%) wastes fuel because the engine has fixed mechanical losses regardless of electrical output. Running above 90% stresses components and can reduce lifespan.
How does altitude affect generator output?
Generators lose approximately 3% of rated output per 1,000 ft above 1,000 ft elevation (5% for natural gas). At 5,000 ft a gasoline generator produces roughly 88% of its sea-level rating. Thinner air means less oxygen for combustion.
How long will 5 gallons of gas run a generator?
It depends on size and load. A 2 kW generator at 50% uses ~0.17 gal/hr (about 30 hours). A 5 kW at 50% uses ~0.42 gal/hr (about 12 hours). A 10 kW at 50% uses ~0.83 gal/hr (about 6 hours). Use the calculator above for your exact setup.