How Long Can a Generator Run? Gas and Propane Run Times

A portable generator can run as long as it has fuel. Champion puts it plainly: the machine can run for as long as it has fuel available, only shutting down for refueling and cooling. On one tank of gasoline, most home backup generators run about 8 to 15 hours at half load. On propane, run time depends on the tank: DuroMax rates its XP9500iH at about 20 hours at half load on a 100 lb cylinder.

Generator run time per tank (manufacturer specs)

Tank size and run times are from each product's specifications (gasoline). Gallons per hour = tank size / hours at 50% load. The DS8000iX and XP9500iH also have demand-based variable idle, which slows the engine at light loads.

How long does a generator run on propane?

Source: DuroStar and DuroMax specifications. Propane holds less energy per gallon than gasoline (91,452 Btu vs 120,214 Btu, per the EIA), so the same generator runs fewer hours per gallon on propane.

Propane tank sizes in gallons

• 20 lb cylinder (grill tank): about 4.6 gallons when full, per AmeriGas.
• 100 lb cylinder: about 23 gallons, per Ferrellgas.
• Large tanks are filled to 80%, so a 500 gallon tank holds about 400 gallons, per AmeriGas.

Estimate for big tanks: the XP9500iH burns a 23 gallon (100 lb) cylinder in 20.25 hours at half load, about 1.14 gallons per hour. At that rate, 400 gallons in a 500 gallon tank would last roughly 350 hours, or about two weeks. A 20 lb grill tank would last about 4 hours. These are our calculations from DuroMax's figures, and real use varies with load and temperature.

How much gas does a generator use?

From the table above, a mid-size home backup generator uses about 0.45 to 0.65 gallons per hour at half load, and a 10,000 to 12,000 watt model about 1 to 1.1 gallons per hour. Running at a quarter load uses about a third to a half less per hour for these models. To cut fuel use, run only what you need and let the generator idle down if it has an economy mode.

Tips for running a generator for days

• Refuel safely. Turn the generator off and, as DuroMax's manual says, allow the engine to cool for several minutes before refueling.
• Use fresh fuel. DuroMax warns that gasoline older than 30 days can permanently damage the fuel system. Use fresh or stabilized fuel.
• Check the oil at every refuel and follow your manual's oil change schedule. Long outages add hours quickly.
• Keep it outside, at least 20 feet from windows, doors, and attached garages, per Ready.gov.
• Running it all night? Read Can You Run a Generator Overnight?

Dual fuel models let you switch to propane when gas stations are closed. Compare fuels in Dual Fuel Generator: Gas vs Propane, or see the full lineup of portable generators.

Need help sizing? Call 1-888-855-7286. Tell us what you want to run and how long your outages last, and we will help you pick a generator and fuel setup.

Generator run time FAQ

How long can a generator run continuously? As long as it has fuel, stopping only to refuel and cool, according to Champion. Check the oil at each refuel.

How long will a generator run on a tank of gas? About 8 to 15 hours at half load for the DuroMax and DuroStar models above, and up to 25 hours at a quarter load.

How long will a generator run on propane? About 9 to 10 hours at half load on a 40 lb cylinder for the DS8000iX and XP9500iH, and about 20 hours on a 100 lb cylinder for the XP9500iH.

How long will a 20 lb propane tank run a generator? Roughly 4 hours at half load on a 7,600 W generator like the XP9500iH, based on our calculation from DuroMax's 100 lb figure. Smaller loads stretch it.

How much gas does a generator use per hour? About 0.45 to 0.65 gallons per hour at half load for a 4,500 to 7,600 watt generator.

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