Here is an example of all the steps in action: If your RV propane tanks holds 14 gallons of propane gas when it’s full, you would multiply 14 X 91,502. The result is 1,281,028. Next you would take this number and divide it by the total BTU demand of any gas appliances you will be using. Keeping with our example, you add up the BTU demand of the stove, water heater, and heater; let’s say the total BTU demand will be 43,800 BTUs. The answer after dividing 1,281,028 by 43,800 is 29. In this case you would have roughly 29 hours of stove, water heater, and heat use before running out of propane.
Another thing to remember is that you will need to keep the outside temperature in mind when calculating gas usage. The colder the weather the faster your propane will get used up. When temps are extremely cold below zero degrees the BTU hourly capacity can be reduced by 50% or more.