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

Here’s the short answer:

A generator on 5 gallons of gas will last **anywhere from 53 minutes to 290 hours and 38 minutes** (for a 30kW propane generator at 100% load to a 500-watt gasoline generator at 25% load, respectively). 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 30,000W gasoline and propane 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:

**Size of the generator**. A bigger 10,000W generator will run out of gas much faster than a small 2,000W generator.**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.**Choice of fuel:**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).*Gasoline vs Propane*.

*Key Note:* We also have to take up generator efficiency into account. Gas generators are not nearly 100% efficient. Rather, as per the generator efficiency and cost analysis here, we can squeeze only about **20%** of the total energy out of gas or propane. According to Wikipedia, car engines have about *28%* efficiency for comparison.

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. If we apply the 20% generator efficiency, we see that 5 gallons of gas give us **36,332 watts** of useful electricity.

*Example:* That’s enough to run a 1,000W generator for 36 hours and 20 minutes at 100% load, or 145 hours and 20 minutes at 25% load (quarter load). If you have a bigger 10,000W generator, 5 gallons of gasoline can run at 100% load for only 3 hours and 38 minutes, or it can run at 25% load for 14 hours and 38 minutes.

**5 gallons of propane** contain 457,500 BTU of energy. That’s 134,048 watts of electrical energy. We know that propane generators are only about 20% effective, giving us **26,810 watts** of actually useful electricity.

*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% load 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 (25% load, 50% load, sometimes even 75% load).

Here is the 5-gallon tank generator calculator. Just pick gas or propane, specified generator wattage, load percentage, and you will get an estimate of how many hours will a generator run on a 5-gallon tank:

## 5-Gallon Tank Generator Running Hours Calculator

Here is how this calculator works:

Let’s say you have an 8,000-watt gasoline generator with a 5-gallon tank. How long will this gasoline generator run continuously on 100% load? Just pick the ‘Gas (Gasoline)’ generator, set the generator wattage to ‘8000’, and the load percentage to ‘100’. Here is the result:

An 8,000-watt gasoline generator will run continuously for **4.54 hours** at 100% load.

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)

Generator Wattage: |
Running Time For Gasoline Generator (100% Load): |
Running Time For Propane Generator (100% Load): |

500-Watt Generator: | 72.66 Hours | 53.62 Hours |

1000-Watt Generator: | 36.33 Hours | 26.81 Hours |

1500-Watt Generator: | 24.22 Hours | 17.87 Hours |

2000-Watt Generator: | 18.17 Hours | 13.41 Hours |

2500-Watt Generator: | 14.53 Hours | 10.72 Hours |

3000-Watt Generator: | 12.11 Hours | 8.94 Hours |

3500-Watt Generator: | 10.38 Hours | 7.66 Hours |

4000-Watt Generator: | 9.08 Hours | 6.70 Hours |

4500-Watt Generator: | 8.07 Hours | 5.96 Hours |

5000-Watt Generator: | 7.27 Hours | 5.36 Hours |

6000-Watt Generator: | 6.06 Hours | 4.47 Hours |

7000-Watt Generator: | 5.19 Hours | 3.83 Hours |

8000-Watt Generator: | 4.54 Hours | 3.35 Hours |

9000-Watt Generator: | 4.04 Hours | 2.98 Hours |

10kW Generator: | 3.63 Hours | 2.68 Hours |

11kW Generator: | 3.30 Hours | 2.44 Hours |

12kW Generator: | 3.03 Hours | 2.23 Hours |

13kW Generator: | 2.79 Hours | 2.06 Hours |

14kW Generator: | 2.60 Hours | 1.92 Hours |

15kW Generator: | 2.42 Hours | 1.79 Hours |

16kW Generator: | 2.27 Hours | 1.68 Hours |

17kW Generator: | 2.14 Hours | 1.58 Hours |

18kW Generator: | 2.02 Hours | 1.49 Hours |

19kW Generator: | 1.91 Hours | 1.41 Hours |

20kW Generator: | 1.82 Hours | 1.34 Hours |

21kW Generator: | 1.73 Hours | 1.28 Hours |

22kW Generator: | 1.65 Hours | 1.22 Hours |

24kW Generator: | 1.51 Hours | 1.12 Hours |

25kW Generator: | 1.45 Hours | 1.07 Hours |

30kW Generator: | 1.21 Hours | 0.89 Hours |

Now you can just use this chart to check how long will your generator run continuously on the 5-gallon tank at 100% load.

*Example:* How long will a 22kW gasoline generator run at 100% load on 5-gallon tank? Just check this chart for the result: It will run for **1.65 hours** (that’s 1 hour and 39 minutes).

Hopefully, you can now adequately estimate how long will a 5-gallon tank run a generator.

If you have any questions regarding the calculations or your specific generator, you can use the comments below, and we’ll try our best to help you out.