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Generator run time calculator
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Method and printable worksheet
Inputs are your assumptions unless a document is supplied. Check source numbers and compatibility in the matching manufacturer manual.
U = supplied fuel - reserve. If 0 < q_low ≤ q_high, runtime interval = [U/q_high, U/q_low]. U=0 yields 0 hours. Rates must be positive, the reserve cannot exceed supply, and units must match. Fuel and load must be supported. Manufacturer runtime can derive q=tank_used/runtime only if actual used fuel amount, load and endpoint are documented; nominal tank size alone is insufficient.
Synthetic arithmetic check: usable fuel 5 gal, consumption 0.4-0.5 gal/h gives 10-12.5 hours, not a product runtime promise.
| Item / exact model | Quantity and units | Low / running | High / starting | Source and date |
|---|---|---|---|---|
| Record 1 | ________ | ________ | ________ | ________ |
| Record 2 | ________ | ________ | ________ | ________ |
| Record 3 | ________ | ________ | ________ | ________ |
Worksheet: https://bestgeneratorforhome.com/how-much-does-it-cost-to-run-a-generator/generator-run-time-calculator/
Review the planning guide. Check the exact manual before using any result. Report a method correction.
The short answer
Generator run time calculator: Runtime equals usable fuel divided by a documented burn rate for your exact model at a stated load. Subtract any reserve first. Rated watts alone cannot produce hours. If no load-specific rate is documented, the honest result is unknown. Piped natural gas runtime depends on supply and is never guaranteed.
Last updated October 2026
What's covered10
- Generator run time calculator data at a glance
- How the generator run time calculator works
- Inputs the tool needs
- Illustrative worked example
- Why published runtime is not always a burn rate
- Fuel type changes the data you need
- Safety limits during long runs
- Sources, method and limitations
- Generator run time calculator FAQs
- Generator run time calculator verdict
A generator run time calculator estimates how many hours a set amount of fuel may last. It needs two things from you. The first is usable fuel. The second is a burn rate for your exact model at a stated load.
Runtime equals usable fuel divided by a documented burn rate. Usable fuel is your supply minus any reserve you keep back. The burn rate must come from your exact model at a stated load. Enter it as a low and high value in the same unit. Divide by the high rate for the short estimate and by the low rate for the long one.
Generator run time calculator data at a glance
The table shows the kind of published runtime data this tool can use. It also shows what each record leaves out. All figures come from manufacturer pages.
| Model and source | Fuel | Load | Published runtime | What is missing for a rate |
|---|---|---|---|---|
| Honda EU2200i | Gasoline, 0.95 gal tank | Rated / quarter | 3.2 h / 8.1 h | Fuel actually used in each test |
| Honda EU3200i | Gasoline | Rated / quarter | 3.3 h / 8.6 h | Tank size and fuel used |
| Honda EU3000iS | Gasoline | Rated / quarter | 6.9 h / 19.6 h | Tank size and fuel used |
| Westinghouse WGen11500TFc | Gasoline | 25% / 50% | 19 h / 9.5 h | Tank size and fuel used |
| Champion 201176 | Gasoline / propane | Stated 25% load | Gasoline 14 h; propane 12 h with a 20-pound cylinder | Actual fuel used and endpoint |
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Read the exact fuel and load point with each runtime value. The hours alone do not provide actual consumed fuel. Preserve those missing-data notes when comparing model claims. They prevent a nominal tank size from becoming an assumed burn rate.
How the generator run time calculator works
The math has two steps. First, find usable fuel. Usable fuel (U) equals the fuel you supply minus any reserve you hold back.
Second, divide by the burn rate range. Enter a low rate and a high rate in the same unit per hour. The runtime range runs from U divided by the high rate to U divided by the low rate.
Some inputs have fixed results. If usable fuel is exactly zero, runtime is zero hours. The tool refuses a zero or negative burn rate. It also refuses a reserve larger than your supply.
It refuses mismatched units, such as gallons of fuel with a pounds-per-hour rate.
If the burn rate is unknown, the result stays unknown. The tool will not guess a number. It also will not turn rated watts into a fuel curve.
Interactive results need JavaScript. Without it, you can still use the formula and a blank printable worksheet. No result shows until you enter valid data.
Inputs the tool needs
Each input should come from a real record, not a guess. Here is the full list.
- Usable fuel and unit. This is fuel you actually have, not just the tank size on a spec sheet.
- Fuel type. Gasoline, propane and natural gas need separate data.
- Exact model. Use the full model number from the manual or product page.
- Low and high burn rate. Both must be in the same unit per hour at a stated load.
- Reserve (optional). The tool subtracts it before any division.
For piped natural gas, the tool does not ask for a tank size. There is no tank to enter. The result describes a supply-dependent duration instead.
Illustrative worked example
This example is synthetic arithmetic. It is not a runtime promise for any product. Say usable fuel is 5 gallons. The burn rate range is 0.4 to 0.5 gallons per hour.
Divide 5 by 0.5 to get 10 hours. Divide 5 by 0.4 to get 12.5 hours. The estimate is 10 to 12.5 hours.
Now add a reserve. If you held back 1 gallon from 6, usable fuel would still be 5. The answer stays the same because the reserve was subtracted first.
Why published runtime is not always a burn rate
A runtime figure alone does not give you a burn rate. You can derive one only when the source states how much fuel was used, at what load, and when the run ended. A nominal tank size is not enough.
Take the Honda EU2200i. Honda lists a 0.95-gallon tank and 3.2 hours at rated load. But Honda does not state that the full tank was burned in that test. So dividing 0.95 by 3.2 would be an assumption, not a documented rate.
The published hours still show how much load matters. The Honda EU3000iS lists 6.9 hours at rated load and 19.6 hours at quarter load. That is about 2.8 times longer. The Westinghouse WGen11500TFc lists 19 hours at 25 percent load and 9.5 hours at 50 percent load on gasoline.
These patterns hold for the listed models only. Do not apply one model's ratio to another engine. Find the record for your own unit.
Fuel type changes the data you need
Each fuel needs its own documented numbers. Tri-fuel output shows why. The Champion 201176 lists 7,250 running watts on gasoline. It lists 6,525 on propane and 5,875 on natural gas.
The current DuroMax XP13000HXT manual lists 10,500 W running on gasoline, 10,000 W on propane and 9,000 W on natural gas. These are output figures, not burn rates. Use fuel-specific burn data to calculate duration.
Match your unit's label and manual revision before sizing loads. Starting watts do not promise a motor will start or state how long peak output lasts.
Propane delivery can be affected by temperature and vaporization. The tool does not model this. Treat a propane result as unconfirmed for very different weather than the source describes.
Piped natural gas depends on service staying available. It is not endless or guaranteed. Fuel pressure, flow and the model's exact fuel instructions are separate checks. Electric watts cannot tell you gas flow.
Gasoline availability during an outage also varies by area.
Safety limits during long runs
A long runtime means more hours outdoors and more refueling. The CPSC carbon monoxide guidance says to run portable engine generators outdoors. Keep them at least 20 feet from homes with exhaust pointed away. Never run one indoors or in a garage, even with the door open.
A tank estimate does not set a safe refueling schedule. The CPSC portable generator safety alert says to shut down the engine and let it cool before adding fuel. Plan that pause before the tank runs out. Keep the unit dry and follow its wet-weather instructions.
A CO alarm means leave for fresh air; do not stay beside the unit to finish a runtime check.
Never backfeed a wall outlet. Home connection needs matched transfer equipment, product instructions and local code. Generac's support guidance says installation belongs to licensed electrical trades. Standby units follow their own manual and local rules for clearance.
Sources, method and limitations
Each manufacturer record retains its exact model, units and published load condition. Your worksheet values are user-entered assumptions or observations identified in source notes. The runtime result is derived arithmetic.
The tool does not independently verify the supplied record.
The tool does not model weather, altitude, wear or load swings. It does not cover battery power stations. Battery runtime uses stored energy in watt-hours, which is a different method. Corrections can be sent through our contact page.
Runtime here is kept apart from dollar cost. To price the same fuel, use the generator running cost calculator. For the bigger picture, read how much does it cost to run a generator.
Generator run time calculator FAQs
Can I estimate runtime from rated watts alone?
No. Rated watts describe output, not fuel use. The tool needs a burn rate for your exact model at a stated load. Without that rate, the result stays unknown.
Look in the owner manual or on the maker's product page for runtime or fuel use tied to a specific load.
Can I use tank size and published runtime to find a burn rate?
Only if the source states the fuel actually used, the load and the endpoint. A nominal tank size is not enough. For example, Honda lists the EU2200i tank and its runtime. Honda does not say the full tank was burned in that test, so we do not derive a rate.
Does propane last the same as gasoline in a tri-fuel unit?
You cannot assume so. Listed output differs by fuel on models like the Champion 201176 and DuroMax XP13000HXT. That means each fuel needs its own burn data. Propane can also be affected by temperature and vaporization, which this tool does not model.
Does piped natural gas give unlimited runtime?
No. Runtime depends on gas service staying available, which is not guaranteed. The tool does not ask for a tank size for piped gas. It reports a supply-dependent duration instead.
Fuel pressure, flow and the model's exact fuel instructions are separate checks from runtime.
Generator run time calculator verdict
Generator run time calculator results depend on the exact inputs below.
If you have a low and high burn rate for your exact model at your planned load, this tool gives a useful hour range. Subtract any reserve first. Keep the units matched.
If you only have rated watts or a tank size, runtime stays unknown. Find a load-specific record before you plan around a number. For piped natural gas, treat the answer as tied to supply, never as a guarantee.
Continue your backup plan
Choose your next step
To put a fuel bill next to the purchase price, read the generator operating cost guide and follow its link to the home generator picks. Match the exact fuel, voltage and starting limits to your result before you choose.