How Long Will A Generator Run On 5 Gallons Of Gas? (Calculator)

Generators stop working when they run out of gas. That’s why we looked into how long will a generator run on 5 gallons of gas.

Here’s the short answer:

A generator on 5 gallons of gas will last anywhere from 6 hours and 42 minutes to 363 hours and 19 minutes. The exact time primarily depends on generator size, and secondarily on the choice of fuel (gasoline vs. propane).

That’s quite a range. How to figure out how long will 5 gallons of gas last in a generator exactly? Well, we need to calculate a bit, based on several factors.

To help you out, we have prepared a ‘5-Gallon Tank Generator Running Hours Calculator’ where you can insert the max. running wattage of your generator, and choice of fuel (gasoline vs. propane), and it will calculate how many hours such a generator lasts on a 5-gallon gas tank. Below the calculator, you will also find a calculated chart of how long does a 5-gallon tank lasts for 500W to 20,000W generators.

Here is what the calculator looks like (you can find it further on):

The 3 most important factors that determine how long will 5 gallons of gas last in a generator are:

1. Size of the generator. A bigger 10,000W generator will run out of gas much faster than a small 2,000W generator.
2. Generator load. If you run a generator on 100% output running wattage, it will burn through the 5 gallons of gas faster than if you would run it on 50% running wattage.
3. Choice of fuel: Gasoline vs Propane. 1 gallon of propane can generate up to 91,500 BTUs. 1 gallon of gasoline can generate up to 124,000 BTUs. That means that a gasoline generator will run 36% longer than a propane generator (if we presume the same energy efficiency).

To adequately calculate the running time of a generator on a 5-gallon gas tank, we need to first determine the energy content of both gasoline and propane:

Energy Content Of Gasoline And Propane

Generators run on either gasoline or propane.

5 gallons of gasoline contain 620,000 BTU of energy. If we convert BTUs to watts (1 BTU = 0.293 Watts), we can get up to 181,660 watts out of 5 gallons of gasoline.

Example: That’s enough to run a 10,000W generator for 18 hours and 10 minutes. If you have a smaller 2,000W generator, 5 gallons of gasoline can run it at 100% load for almost 91 hours; that’s almost 4 days.

5 gallons of propane contain 457,500 BTU of energy. That’s 134,048 watts of electrical energy.

Example: With a 5-gallon propane tank, we can run a 10,000W generator for 13 hours and 24 minutes. A smaller 2,000W generator can use that energy to run for 67 hours and 1 minute; almost 3 days.

Standard generators do give 100% output all the time. Inverter generators, on the other hand, adjust the power output to the power draw; they will last longer on a 5 gallon of gas.

5-Gallon Tank Generator Running Hours Calculator

Using this calculator, we can calculate exactly how long will a 5-gallon tank last for different generator sizes:

Calculated Table For Different Generator Sizes (5-Gallon Tank)