SettingsSettings for this calculationUS
The generator's fuel tank size.
Portable generators commonly have 4-8 gallon tanks; standby generators connected to natural gas or a large propane tank aren't limited this way.
Check the manufacturer's fuel consumption chart at your expected load percentage.
Consumption rate varies significantly with load — running at 50% load uses noticeably less fuel per hour than running near full capacity. Switch the unit beside the field to match whichever way your chart is printed: North American generators quote US gallons per hour, and most others quote litres per hour.
Estimated runtime
6.67 hours
Actual runtime varies with load percentage, fuel type, temperature, and altitude — check your specific generator's published fuel consumption chart at your actual expected load for a more precise figure.
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Generator Fuel Runtime Calculator: 6.67 hours — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Runtime (hours) = fuel tank capacity (gallons) / fuel consumption rate (gallons per hour) at the expected load
Inputs used
- Fuel Tank Capacity
- 5 gal
- Fuel Consumption Rate
- 0.75 gal/hr
Confidence note: Actual runtime varies with load percentage, fuel type, temperature, and altitude — check your specific generator's published fuel consumption chart at your actual expected load for a more precise figure.
What this calculation does not cover
- Treats the burn rate as constant for the whole run. Real load moves as pumps, fridges and heaters cycle, so this holds only if the rate you entered is the average across the run rather than the figure at one load point.
- Assumes every drop in the tank reaches the engine. Fuel pickups sit above the tank floor, low-fuel cut-out and surging arrive before a tank is dry, and a propane or LPG vessel is filled to a working fraction of its nameplate size — usable fuel is always less than stated capacity.
- No derate for site or engine condition. Altitude, intake air temperature, fuel type and a worn or poorly serviced engine all move consumption away from the manufacturer's chart, which is measured on a new set under test conditions.
- This is not a sizing or load calculation. It does not check that the generator can carry the load you intend to put on it, and it cannot tell whether the burn rate you entered matches that load — read the rate off the consumption chart at the load percentage you will actually run.
- Ignores the stops a long run needs. Oil-level checks and oil-change intervals on portable sets arrive well before a large tank empties, and refuelling means shutting the engine down and letting it cool. The hours here are fuel-limited, not the hours the machine will run unattended.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations1
- Runtime (hours) = fuel tank capacity (gallons) / fuel consumption rate (gallons per hour) at the expected load
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