Generator Runtime Calculator
Knowing how long a generator can run on the fuel in its tank helps when you plan for an outage or a job site. This estimates run time from the tank size and the fuel the unit burns each hour.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Run time is the usable fuel divided by the fuel used per hour. Usable fuel is the tank size times the share you enter, because some fuel stays in the tank and the pump stops drawing before it is empty.
Fuel use rises with load. Check the maker's fuel chart for a load close to yours, and enter that hourly figure here.
Worked example
A 5 gal tank with 90% usable, burning 0.5 gal an hour, runs for about 9 h.
Questions
Why is the usable share below 100 percent?
Pumps and fuel lines usually stop drawing before the tank is empty, so a lower share gives a more cautious number.
Does run time change with load?
Yes. A heavier load burns more fuel per hour, so the run time is shorter. Enter the hourly use for the load you expect.
Where do I find the fuel use?
The maker's manual or spec sheet usually lists fuel use at a few loads. Use the figure closest to your own load.
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