A 20 lb tank doesn’t hold 2.4 gallons of propane. That is a misconception because a 20 lb tank can indeed hold 2.4 gallons of water. **Propane is different**; it has a different *density* and you can’t really put 20 lb of propane in a 20 lb propane tank.

To adequately determine how many gallons of propane are in a 20 lb tank, you have to use these 2 rules:

**80% propane tank rule.**Namely, every propane tank is filled up to 80% of its total capacity.*Example:*A 20 lb tank doesn’t hold 20 lb of propane. Rather, it contains 16 lb of propane. This is a safety requirement.**How much does a gallon of propane weigh in pounds (lb)?**Propane density depends on temperature: at 90°F, a gallon of propane weighs 4.05 lb, and at 60°F a gallon of propane weighs 4.20 lb. You can consult how much propane weighs here.

In most cases, we use a median propane density (4.11 lb/gallon) to calculate how many gallons does a 20 pound propane tank hold.

Here is how you calculate that:

## How Many Gallons Is A 20 Lb Propane Tank?

Using the 1st rule, you can see that a full 20 lb propane tank can hold at most 16 lb of propane.

Now you have to account for propane density (2nd rule) and calculate the volume of propane in a 20 lb tank like this:

**Gallons Of Propane = Weight Of Propane / Propane Density**

In the case of 20 lb tank, we get this result:

**Gallons Of Propane **= 16 lb / 4.11 lb/gallon =** 3.89 Gallons**

Here you have it:

A 20 lb propane tank can hold **3.89 gallons of propane**. This is about *4 gallons*.

If you know these two rules, you can calculate how many gallons of propane does a propane tank hold for pretty much any tank size.

Hope this helps. If you have additional questions about how many gallons are in propane tanks, you can use the comments below and we’ll try to help you out.