Generator Fuel Tank: Capacity vs Run Time

What a Listing Shows: Tank Capacity and Run Time

A generator listing usually gives two separate figures for fuel. Tank capacity is how much fuel the tank holds, often stated in gallons. Run time is the number of hours the maker says the generator will run on a full tank at a stated electrical load. The two figures are related but not the same: capacity is a storage measure, and run time is a result of that capacity combined with the load the generator is delivering.

The run time figure is meaningful only with the load it belongs to. A listing may show more than one run time because the load differs. When you compare two generators, compare run times stated at the same load; otherwise the figures are not alike. The maker's page is where the full run time figures and their loads are listed.

For the general relation between fuel and run time, see run time per gallon.

Why Tank Capacity Matters

Tank capacity tells you how much fuel is on board before you refuel. At the same load, a larger tank holds more fuel, so the generator runs longer before the tank needs refilling. That relationship is not a promise about your exact run time: the load you place on the generator decides how quickly the fuel is used.

For a home that has a propane tank, a dual fuel generator accepts both gasoline and propane. Gasoline is a fuel made from crude oil and other petroleum liquids, per the EIA, and propane is a hydrocarbon gas liquid. Which fuel you can get during an outage is a question for your fuel supplier. See dual fuel generators.

How Load Changes Run Time

Run time falls as load rises. At a higher electrical load, the engine works harder and uses fuel more quickly. At a lower load, it uses less fuel and runs longer. So a run time figure is always tied to a load: the same generator can show a longer run time at a lower load and a shorter run time at a higher one.

This is why reading the load on a listing matters. The site's buying guides group generators by watts, including starting and running watts, but they do not add run time figures. See running watts vs starting watts and the mid-size generator guide.

Comparing Two Generators by Tank and Run Time

To compare two generators, look at three things together: tank capacity, fuel type, and run time at a stated load. A gasoline-only generator and a dual fuel generator use different fuels, so their run time figures are not directly comparable unless the fuel and the load are the same.

The listing is a summary. The maker's page is where the conditions behind the figures are stated. If a listing does not say the load for a run time figure, check the maker's page or ask the maker. This site does not fill in missing figures.

Fuel Words on a Listing

Titles and spec sheets use fuel words like gasoline, dual fuel, and tri fuel. Gasoline is a petroleum product, per the EIA. Propane is a hydrocarbon gas liquid, and natural gas is a fossil fuel. A dual fuel generator runs on gasoline and propane; a tri fuel model adds natural gas. Which fuel you choose is a shopping question about what your household can receive during an outage.

A home on a propane tank often starts with a dual fuel question; a home with natural gas service has a fuel question for the service provider. See fuel type comparison and the rural Texas generator guide.

Texas Shopping Questions

Before winter storm season or summer heat, think about how long you want a generator to run and how you plan to refuel. Those are planning questions, not figures this site can give. The Texas Division of Emergency Management and Texas Ready publish preparedness guidance for households; both are good starting points.

Connection to your home's wiring, the size of the generator for your appliances, and fuel availability are questions for a licensed electrician, the generator maker, and your fuel supplier. The local permit office decides permit questions. See the Texas backup power overview to compare types.

What to Check on the Listing and the Maker's Page

Before buying, check the listing's stated figures, then compare them with the maker's page. Look at the run time figure together with the load it is stated for, and check the fuel type. The maker's manual describes how the generator is meant to be used, stored, and serviced between seasons; follow the manual.

A licensed electrician and the local permit office decide how a generator connects to your home. This site does not give connection, wiring, or installation steps. For an automatic whole-house unit, see the whole house generator guide.

What to pick for your situation

Questions

What is fuel tank capacity on a generator listing?

Tank capacity is how much fuel the generator's tank holds, usually stated in gallons. It is a storage measure and appears separately from the run time figure.

What does run time mean on a generator listing?

Run time is the number of hours the maker states the generator will run on a full tank at a given electrical load. The load is part of the statement, so the figure is only meaningful with the load it belongs to.

Why does the same generator show more than one run time figure?

Because run time changes with load. A lower load uses fuel more slowly, so the generator runs longer; a higher load uses fuel more quickly. Listings may state run times at different loads.

How do I compare run time between two generators?

Compare run times stated at the same load, and check that the fuel type is the same. If the fuel or the load differs, the run time figures are not directly comparable.

Does a bigger tank guarantee a longer run time?

At the same load, a bigger tank holds more fuel, so the generator runs longer before refueling. The load you draw decides how quickly the fuel is used, so run time is not guaranteed by tank size alone.

Where do I find the run time figures for a generator?

The listing and the maker's page both state them. The maker's page also states the load conditions. This site does not add its own run time or fuel use figures.