How long can a generator run?
Published October 6, 2026.
Built by Jeremy Panasuk.
A tank time is a test at a stated load. An oil change is a separate clock. This site's gallons-per-hour rule is neither of those tests.
Two published tank times
Use the sentence that names the load. On the EU2200i specifications page, rated output is 1,800 W and maximum is 2,200 W. Run time per tankful is 3.2 hours at rated load and 8.1 hours at quarter load. Fuel tank capacity is 0.95 gallon. Quarter load of the 1,800 W rating is 450 W. The page does not say the 8.1 hours is at 50%.
Honda's explainer lists the EU2200i as "runs up to 8.1 hours" next to "2200 watts," and it does the same style of line for other models: EU1000i up to 6.8 hours at 1,000 watts, EU3200i up to 8.6 hours at 3,200 watts, EU3000iS up to 20 hours at 3,000 watts, and EU7000iS up to 16 hours at 7,000 watts. Those lines do not say 25% or 50%. The 8.1-hour figure that matches a stated load is the specifications page's quarter-load line, not the explainer's "up to" line.
The GP6500 product listing (model 7672-3) prints fuel tank capacity 7.9 gallons, run time at 25% of 16.5 hours, and run time at 50% of 11.5 hours. Running watts on that listing are 6,500. Fifty percent of 6,500 W is 3,250 W. The owner's manual also prints a run time at 50% load in the engine section that this site's storm page already quotes as 11.5 hours for that section. This page attributes 16.5 hours at 25% and 11.5 hours at 50% to the GP6500 product listing, not to the GP8000E column. More manufacturer tank lines, each with the load the page stated, are on the portable generator watts chart.
Why the site's ÷7,000 rule is not that test
The home calculator sets gasoline gallons per hour equal to recommended watts ÷ 7,000. The storm runbook uses running watts ÷ 7,000. Neither button is Generac's tank test.
Fifty percent of the GP6500's 6,500 W running rating is 3,250 W. This site's rule on those 3,250 W is 3,250 / 7,000 = 0.464 gallons per hour. The listing's 50% test on a 7.9 gallon tank lasts 11.5 hours, which is 7.9 / 11.5 = 0.687 gallons per hour. The test burns more per hour than the rule of thumb. Use the listing when you are asking how long that GP6500 ran in Generac's 50% test. Use the calculator when you are asking how this site turns a watt recommendation into a planning volume. Propane on the home calculator is a further step, × 1.37, on how much propane a generator uses.
Oil is a second clock
The Honda EU2200i owner's manual says to change the engine oil at the first month or 20 hours, then every 6 months or 100 hours, whichever comes first. Generac's GP6500/GP8000E manual says to change oil after the first 30 hours, then every 100 hours or every year. One GP6500 tank at the listing's 50% run time is 11.5 hours. That is under both first-change marks. Two of those tanks are 23.0 hours, which passes Honda's 20-hour first change and not Generac's 30-hour first change. Three of those tanks are 34.5 hours, which passes Generac's 30 hours. The storm runbook and the 5-year cost tool count those same hour marks. They do not add a rule that the engine must shut down when the tank is empty beyond what the manual's oil schedule and the tank itself already say.
Run the generator outdoors only, at least 20 feet from the house, never inside, including a garage with the door open (CPSC). A longer tank time is not permission to move the set closer.
Compiled with AI assistance from the sources below. Spot an error? Email [email protected].