Calculating Propane Usage

It's always nice to know how long your propane will last if you are out and about. And this is some quick math to get an estimate.

How Long Will My Propane Last?

Getting a good estimate

It's always nice to know how long your propane will last if you are out and about. And this is some quick math to get an estimate.

The Basics

The first piece of the puzzle is knowing how much propane is in your RV cylinders or tank when full. Remember an RV propane cylinder or tank is full at 80% of its capacity to allow for expansion. Wait until your cylinder or tank is nearly empty and the next time you have it filled ask the attendant how much it holds.

The dimensions presented below are approximate measurements of common size propane cylinders found in service today. The measurements are not exact so contact your propane company or container manufacturer for precise cylinder dimensions.

  5# 10# 20# 30# 40#
Capacity (gallons) 1.2 gal 2.4 gal 4.7 gal 7.1 gal 9.4 gal
Weight (empty) 4 lbs 13.3 lbs 18 lbs 24 lbs 29 lbs
Weight (full) 9 lbs 23 lbs 38 lbs 54 lbs 70 lbs
Overall Height 12 inches 17.43 inches 18 inches 24 inches 29 inches
Diameter 8.00 inches 8.87 inches 12.5 inches 12.5 inches 12.5 inches
BTU Capacity 107,740 215.807 430,270 649,980 860,542

The Math

The next piece needs some basic propane BTU numbers - 91,502 BTUs per gallon and 21,548 BTUs per pound

Multiply your propane container capacity using one of these BTU formulas, (gallons or pounds), to determine the container BTU capacity.

Now, divide your container BTU capacity by the total BTU demand of the LP gas appliances you plan to use. [ BTU appliance demand can normally be found on the appliance itself, or in the appliance owner's manual. ]

The result will will be an estimate of how long you can expect your LP gas to last.

Example: If your RV propane container holds 14 gallons of LP gas when it's full, you multiply 14 X 91,502. The result is 1,281,028. Now divide this figure by the total BTU demand of any LP gas appliances you will be using. Let's say, for the sake of an example, the total BTU demand will be 43,800 BTUs. In this case you would have approximately 29 hours of use before running out of LP gas.

Why an estimate? Because there are some variables that may affect the numbers.

The amount of LP gas in the container and varying temperatures will affect these calculations. This is especially true in cold weather. At temperatures below zero degrees the per hour container BTU capacity will be reduced by 50% or more.

Calculating propane usage can give you a general idea of how long you can use your LP gas fired appliances before needing to find a propane filling station.