What Is the Propane Tank Usage Calculator?
This calculator estimates how long a propane tank will last when powering a single appliance. It works for grills, patio heaters, generators, furnaces, water heaters, and camping gear. By combining the amount of propane in your tank with the energy demand of your appliance, you get a clear estimate of run time in both hours and days.
How to Use It
Enter two numbers: the gallons of propane in your tank and your appliance's heat output in BTU per hour. A standard 20 lb grill tank holds about 4.6 gallons, a 100 lb tank about 23.6 gallons, and a 500 gallon home tank is typically filled to roughly 400 gallons (80%). The appliance's BTU/hour rating is printed on its label or in the manual.
The Formula Explained
One gallon of liquid propane provides approximately 91,500 BTU of energy. To find how long a tank lasts, multiply the gallons by 91,500 to get the total available energy, then divide by the appliance's hourly BTU consumption:
$$\text{hours} = \frac{\text{gallons} \times 91{,}500}{\text{BTU per hour}}$$
Dividing the result by 24 converts it to days of continuous operation.
Worked Example
Suppose you have a 20-gallon tank running a 30,000 BTU/hour space heater. Total energy is \(20 \times 91{,}500 = 1{,}830{,}000\) BTU. Dividing by 30,000 gives 61 hours, or about 2.54 days of continuous use.
$$\text{hours} = \frac{20 \times 91{,}500}{30{,}000} = 61$$
FAQ
How many BTU are in a gallon of propane? About 91,500 BTU per gallon of liquid propane. This is the figure used here.
Does a 20 lb grill tank equal 20 gallons? No. A 20 lb tank holds about 4.6 gallons of propane, not 20. Enter the actual gallons, not the tank's weight rating.
Will my tank last exactly this long? This is an idealized estimate assuming constant full output. Real run time varies with appliance efficiency, thermostat cycling, ambient temperature, and partial-load operation.
