How Much Propane Do Generators Use Per Hour? (500W – 40kW)

Figuring out generator propane usage is notoriously hard. You usage get “This propane generator can run up to 20 hours on a full tank (at 25% output)”; no one can actually tell you how much propane a generator use.

We are going to tackle this problem using a little bit of math. In the end, you will know exactly how many gallons of propane generators use per hour at 25%, 50%, 75%, and 100% rated loads.

To help you out, we have included a Generator Propane Usage Calculator as well as Generator Propane Usage Chart for 500 watts to 40 kW propane generators further on.

Quick outtake: Generators can use anywhere from 0.02 to 6.69 gallons of propane per hour. This data is for a small 500W generator running at 25% load and a big whole house 40kW generator running at 100% load (full load), respectively.

First, however, we have to address the one thing that makes figuring out how much propane generators use so incredibly hard: propane generator efficiency.

Theory: Calculating how much propane generators use should be fairly easy. Here are the basic metrics we need to calculate generator propane usage:

• 1 gallon of propane contains 91,452 BTU of energy content, according to the US Energy Information Administration (EIA).
• To produce 1 kWh of electricity, we need 3412 BTU of energy.

That means that, at 100% efficiency, a propane generator could produce 26.80 kWh of electricity per gallon of propane. Here are some theoretical calculations:

• A 10kW generator should run for 2.68 hours per gallon of propane (100% output). In reality, a 10 kW generator will run for about 32 minutes on a gallon of propane.
• A 20kW generator should run for 1.34 hours per gallon of propane (100% output). In reality, a 20 kW generator will run for about 16 minutes on a gallon of propane.
• A 24kW generator should run for 1.12 hours per gallon of propane (100% output). In reality, a 20 kW generator will run for about 13 minutes on a gallon of propane.

Why is such a discrepancy between how long should a generator run per gallon of propane, and the practical running time?

One word:

Efficiency.

Practice: Propane generators are not 100% efficient (not even close). However, if we can figure out propane generator efficiency, we can quite easily calculate how much propane generators use. This includes:

• How many gallons per kWh propane generators use?
• How long will a generator run on a gallon of propane?
• How long will a propane generator run on a full propane tank?

Here is the full formula for propane generator propane usage:

Generator Propane Usage = Propane Generator Size × Rated Load × Running Hours /  (26.80 kWh/Gallon × Propane Efficiency)

We know what size propane generator we have (1000W, 10kW, 22kW, etc.), we also know that rated loads can be 25%, 50%, 75%, or 100%, and we know how long we will run a generator (or we can calculate propane usage per hours). What we don’t know (and have to determine) is the propane efficiency.

The reason why it is so notoriously hard to answer how much propane generators use is that we don’t have a standardized measurement of propane generator efficiency.

That’s we will first pull propane generator efficiency data to estimate the average propane generator efficiency:

Propane Generator Efficiency

Nowhere on the propane generator specification sheet will you find generator efficiency. This is the most elusive metric for propane generators.

The one study of propane generator efficiency that we can pull data from is the UGOV technical commentary on the efficiency of portable generators.

Within this document, we can find the measured efficiency rating for a propane-powered Generac RG022 22kW generator. Here are the outlined efficiencies:

• 22.3% propane efficiency at 100% rated load.
• 21.0% propane efficiency at 75% rated load.
• 18.6% propane efficiency at 50% rated load.
• 19.8% propane efficiency at 25% rated load.

First of all, we can see that propane efficiency ranges between less than 20% and up to about 25%. Do note that the efficiency at lower loads tends to be lower (22.3% efficiency at 100% load vs. 19.8% efficiency at 25% load).

We can use these efficiency rates as the benchmark rates for calculating how many gallons of propane per hour propane generators use.

Before we check out the calculator and the accompanying chart, let’s manually calculate propane usage for

How Much Propane Does A 20kW Generator Use Per Hour? (Example)

Alright, a 20kW generator will generate 20 kWh of electricity per hour (at 100% rated load). How much propane will it use for that?

We use the generator propane usage formula from above:

Generator Propane Usage = Propane Generator Size × Rated Load × Running Hours /  (26.80 kWh/Gallon × Propane Efficiency)

We input all the relevant information that we now have: 20kW propane generator size, 100% rated load (factor 1.00), 22.3% efficiency (factor 0.223), and 1 running hour. Let’s input all these metrics in the equation like this:

20kW Generator Propane Usage = 20kW × 1.00 × 1h / (26.80 kWh/Gallon × 0.223) = 3.35 Gallons Per Hour

As you can see, the 20kW generator will use 3.35 gallons per hour at 100% load. Here are calculations for 20kW generator propane usage for 25%, 50%, and 75% loads as well:

• 0.94 gallons per hour at 25% load, producing 5 kW of electric output.
• 2.01 gallons per hour at 50% load, producing 10 kW of electric output.
• 2.67 gallons per hour at 75% load, producing 15 kW of electric output.

This is just one example.

You can use the following calculator to estimate how much propane will your generator use per hour. Below the calculator, you will also find propane usage per hour for 500W, 1000W, 1500W, 2000W, 2500W, 3000W, 4000W, 5kW, 6kW, 7kW, 8kW, 9kW, 10kW, and up to 40kW generators running at 25%, 50%, 75%, and 100% rated loads.

Propane Generator Usage Calculator

In this calculator, just insert the propane generator size (in kW) and choose the load (25%, 50%, 75%, or 100%). The calculator will automatically calculate how much propane will your generator use per hour:

Here is how to use this calculator:

Let’s say that we have a 10kW propane generator and want to know how much propane will it use at full load (100%). You just slide the slider to ’10’, choose the ‘100%’ option and you get the result: Running a 10kW at full load will use 1.67 gallons of propane per hour.

To help you out, we have calculated generator propane use per hour for different generators and at all 4 loads, and summarized the results in this neat chart:

Propane Per Hour Chart For Propane Generators

With this chart, you can get quite a good idea of how many gallons per hour will a propane generator use.

Let’s look at a 22kW generator as an example. You can see that the 22kW propane generator will consume:

• 1.04 gallons of propane per hour at 25% load.
• 2.21 gallons of propane per hour at 50% load.
• 2.93 gallons of propane per hour at 75% load.
• 3.68 gallons of propane per hour at 100% load.

Using the calculator and this chart, you can now adequately estimate propane generator usage per hour. If you have any questions or would like for us to calculate propane consumption for you, you can use the comment section below. Give us some numbers, and we’ll try to help you out.