Generator Fuel Calculator
Running time is the fuel you have divided by the rate the engine burns it, and fuel needed is the same rate multiplied by the hours you need — so both answers stand on one number, and the only honest version of it is one the manufacturer published. Honda, Generac and Champion each state a tank capacity and a run time per tankful at a named load for the models below; this calculator derives the rate from that pair and nothing else. Pick a model and a published load, then either enter the fuel you have to get hours, or the hours you need to get gallons and an optional cost. If your generator is not listed, enter the consumption figure from your own manual instead.
Two questions on one rate
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Data last updated: 2026-10-06
The switch at the top of the calculator chooses the question. "How long will my fuel last?" divides the fuel you enter by the rate. "How much fuel do I need?" multiplies the hours you enter by it, and adds a cost if you give a price. The result always names the rate it used and where that rate came from.
When the fuel involved is more than the selected model's tank, the calculator says so rather than presenting a continuous run: it counts the tankfuls and the refuelling stops, and it does not add time for refuelling, because no manufacturer publishes how long that takes.
Models with published figures
These are the models whose tank capacity and run time were read from the manufacturer's own pages or owner's manuals. A model qualifies only when the manufacturer publishes both figures and names the load the run time was measured at. The rate in brackets is the tank divided by that run time — the same arithmetic the calculator runs, shown so it can be checked by hand.
| Model | Rated output | Tank | Published run time (derived rate) |
|---|---|---|---|
| Honda EU2200ITAN | 1,800 W (2,200 W max) | 0.95 US gal | 8.1 h at 1/4 load (0.117 gal/h); 3.2 h at rated load (0.297 gal/h) |
| Honda EU3200IAN / EU3200IAC | 2,600 W (3,200 W max) | 1.2 US gal | 8.6 h at 1/4 load (0.140 gal/h); 3.3 h at rated load (0.364 gal/h) |
| Honda EU7000ISNAN / EU7000ISNAC | 5,500 W (7,000 W max) | 5.1 US gal | 16.0 h at 1/4 load (0.319 gal/h); 6.4 h at rated load (0.797 gal/h) |
| Honda EB5000 | 4,500 W (5,000 W max) | 6.2 US gal | 10.5 h at 1/2 load (0.590 gal/h); 7.1 h at rated load (0.873 gal/h) |
| Honda EB10000 | 9,000 W (10,000 W max) | 8.19 US gal | 7.9 h at 1/2 load (1.037 gal/h); 5.4 h at rated load (1.517 gal/h) |
| Generac GP2500i | 2,200 W (2,500 VA surge) | 1.0 US gal | 4.0 h at 50% load (0.250 gal/h) |
| Generac GP3500iO | 3,000 W (3,500 W starting) | 2.37 US gal | 8.0 h at 50% load (0.296 gal/h) |
| Generac iQ3500 | 3,000 W (3,500 W starting) | 2.64 US gal | 8.0 h at 50% load (0.330 gal/h) |
| Generac GP6500 / GP6500E | 6,500 W (8.125 kVA surge) | 7.9 US gal | 11.5 h at 50% load (0.687 gal/h) |
| Generac GP8000E | 8,000 W (10.0 kVA surge) | 7.9 US gal | 10 h at 50% load (0.790 gal/h) |
| Champion 100705 (2000W Inverter) | 1,600 W (2,000 W starting) | 1.1 US gal | 11 h at 1/4 load (0.100 gal/h) |
| Champion 201317 (2500W Inverter) | 1,850 W (2,500 W starting) | 1.05 US gal | 11.5 h at 1/4 load (0.091 gal/h) |
| Champion 100809 (4000W Inverter) | 3,000 W (4,000 W starting) | 1.54 US gal | 10 h at 1/4 load (0.154 gal/h) |
| Champion 201071 (3650W Generator) | 3,650 W (4,550 W starting) | 4.7 US gal | 14 h at 1/2 load (0.336 gal/h) |
| Champion 201094 (5500W Generator) | 5,500 W (6,875 W starting) | 7.7 US gal | 11 h at 1/2 load (0.700 gal/h) |
| Champion 201074 (8000W Electric Start Generator) | 8,000 W (10,000 W starting) | 7.7 US gal | 10 h at 1/2 load (0.770 gal/h) |
| Champion 201160 (12,000W Electric Start Generator) | 12,000 W (15,000 W starting) | 11 US gal | 9 h at 1/2 load (1.222 gal/h) |
The manufacturers do not all publish the same load points. Honda gives two per model — a quarter or half of rated output, and rated output — while Generac's manuals give 50% only and Champion's specification tables give one point — a quarter load for the inverter models here and a half load for the conventional generators. The calculator offers each model exactly the points its manufacturer published, so some models show one load and some two. The rated figure is the one used for the load, never the starting or surge maximum.
Two worked examples
How long will it last? A Honda EU2200ITAN holds 0.95 US gal, and Honda publishes 8.1 hours at a quarter of rated load: 0.117 gallons an hour. Two five-gallon cans — 10 US gal — at that rate is about 85 hours of running time. It is not 85 hours of continuous running. Ten gallons is a little over ten tankfuls, so the engine is stopped and refuelled about ten times along the way, and the manual requires it to be stopped and cooled first each time.
How much will it need? A Honda EU7000iS at a quarter load burns 5.1 gallons in 16 hours, 0.319 gallons an hour. A 24-hour window needs about 7.65 gallons, which is about 1.5 tankfuls and one refuelling stop; at $3.90 a gallon that is about $30. At rated output the same 24 hours needs about 19.1 gallons — 3.75 tankfuls, three refuelling stops, about $75. Nothing about the generator changed except what it was asked to carry.
What the estimate leaves out
Maintenance stops, oil checks, a load that changes through the night, ambient temperature and altitude are all outside it. So is the economy-throttle behaviour that makes a quarter-load figure achievable in the first place: a generator held at a heavier load burns more than its quarter-load rate. The result is a planning figure for how much fuel to have on hand, not a schedule to run to, and it is not a suggestion that a running generator can be left unattended.
Fuel this calculator does not handle
Propane and natural gas are out of scope. They are sold and metered in different units — pounds, gallons of liquid, therms, cubic feet — and a standby unit on a utility gas line has no tank to divide by at all. Every preset here is a gasoline-only model with a gasoline figure. Diesel and gasoline work in custom mode with a consumption figure from your own manual at a stated load; there is no universal diesel coefficient, because there is no universal diesel engine.
Sizing is a different question
The generator wattage calculator answers whether a generator is large enough: it adds the running watts of what you want on it and finds the single largest starting surge. Those are peak figures, and a peak is not an average. A house that needs 5,000 W of capacity does not draw 5,000 W all night, so a sizing total must not be fed into a fuel rate as if it were a steady load. Size the generator there; plan the fuel here, against a load the manufacturer actually published. For what the same appliances would cost on utility power, the electricity cost calculator uses EIA's state average rates.
- Running a generator indoors, in a garage, or anywhere the exhaust can reach a living space: never, under any conditions. CO from a portable generator can be lethal within minutes.
- Refuelling: stop the engine and let it cool first, per the manufacturer's manual, and wipe up spilled fuel before restarting.
- Storing fuel for a long outage: approved containers, away from the house and from any ignition source, in the quantity your local fire code allows.
- Connecting a portable generator to house wiring: through a transfer switch or an interlock installed by a licensed electrician, never a cord into an outlet.
- Any plan that depends on a generator for medical equipment: talk to the equipment supplier and your utility, not a calculator.
Frequently asked questions
How accurate is the answer?
At the load the manufacturer published, it reproduces the manufacturer's own figure exactly, because it is derived from that figure. Real consumption moves with load, temperature and altitude, so treat the answer as a planning estimate rather than a measurement of your unit.
Why can't I pick any load I like?
Because each manufacturer publishes run time at specific loads only, and a figure between two published points would be an interpolation wearing the manufacturer's name. The calculator offers only the points in the specification — two for the Honda models, one for the Generac and Champion models here.
Can I use this for a propane or natural gas generator?
No. Propane and natural gas are sold and metered in units this calculator does not handle, and a standby generator on a utility gas line has no tank at all. The presets are gasoline figures; custom mode takes gasoline or diesel with your own consumption figure.
My generator isn't listed. What do I do?
Use custom mode. Find the consumption figure in your own manual — it will be stated at a particular load — and enter it with the matching units. The arithmetic is identical; only where the rate comes from changes, and the answer is only as good as the figure you entered.
Is 24 hours of fuel the same as 24 hours of running?
No. On most models here a 24-hour window is more than one tankful, so it includes refuelling stops, and the manual requires the engine to be stopped and cooled before each one. The calculator counts the tankfuls and the stops whenever the fuel exceeds the tank.
What price should I enter?
Whatever you actually pay locally. The calculator holds no fuel price of its own, because a price would be stale within a week and wrong by region within a day. Leave the field blank and it simply returns the quantity.