Propane tanks come in many sizes and can have different units of measurement making it confusing to understand how many gallons are actually inside the tank. Some of the smaller and more common sizes are referred to by the weight of propane they contain rather than gallons, such as a 20lb propane tank which you will commonly have around a house for BBQs, heaters, etc. A 20 lb propane tank contains 4.7 gallons of propane and weighs just under 40lbs when full. Larger sizes that have more extensive use like supplying energy for a home such as 250 gallons and 500 gallons are measured by their total gallon capacity and not the amount of propane inside.
Regardless of propane tank size, all tanks are only filled to around 80% of their total size. This can lead to some confusion on exactly how much propane is inside a tank. This can be crucial if you’re trying to calculate how long your tank can last you and when you’ll need to refill, as well as figuring out the total weight of the tank.
To further add to this confusion, some propane suppliers such as Blue Rhino & Amerigas only fill their 20lb propane tanks to 15 lbs of propane. So if you’re exchanging a tank with these companies, you’re tank is only being filled to roughly 66% of its total capacity as opposed to the full 80% that is legally allowed. I’ll expand on this further below.
Propane Gallon Calculator
Below I have created a calculator you can use to figure out how many gallons of usable liquid propane is inside your propane tank.
Calculate Gallons of Propane in a Lb Tank
Portable Sizes (Measured in Lb.s)
Listed below are the common sizes of propane tanks and their respective level of propane in gallons. Remember smaller sizes are measured by the weight of propane it contains.
Propane tanks labeled by their weight typically have ~23% of their labeled weight in gallons of propane. (ex. 20lb propane tanks have 4.7 gallons of propane)
| Tank Size | Gallons Usable | Total BTU |
| 1lb | 0.23 | 21,045 |
| 2lb | 0.47 | 43,005 |
| 5lb | 1.17 | 107,055 |
| 10lb | 2.35 | 215,025 |
| 15lb | 3.52 | 322,080 |
| 20lb | 4.70 | 430,050 |
| 30lb | 7.05 | 645,075 |
| 40lb | 9.40 | 860,100 |
| 50lb | 11.75 | 1,075,125 |
Household Sizes (Measured in Gallons)
Lastly, listed below are the more common sizes of propane tanks for household use and their respective level of propane in gallons. Larger tanks like these usually are not referenced by their weight in propane but by total gallon storage. But remember that propane tanks are never filled more than 80% so there is still some difference in the tank size and actual amount of propane inside.
Propane tanks labeled by their gallon capacity typically have ~80% of their labeled capacity in gallons of propane. (ex. 500 gallon tanks hold 400 gallons of propane)
| Tank Size (Gallons) | Gallons Usable | Total BTU |
| 120 | 96 | 8,784,000 |
| 250 | 200 | 18,300,000 |
| 300 | 240 | 21,960,000 |
| 400 | 320 | 29,280,000 |
| 500 | 400 | 36,600,000 |
| 1,000 | 800 | 73,200,000 |
| 2,000 | 1,600 | 146,400,000 |
BTUs In A Gallon of Propane
A gallon of propane contains roughly 91,500 BTU. This can be useful to know if you need to calculate how many total BTUs your propane tank contains so you can figure out how long it can run an appliance. For example, if you wanted to figure out if a full 20lb propane tank could run a 15,000 BTU pizza oven at an event you could calculate how many BTUs the tank has and how many BTUs the oven consumes per hour to find out if you’ll need to refill.
The calculation would be:
(20*0.235*91,500)/15,000=28.67
So a 20lb propane tank can run a 15,000 BTU pizza oven for 28.67 hours.
Propane Tank Running Time Calculator
Below is a simple calculator I made to help you determine how long a propane tank can run any BTU size appliance. Please note this calculator is only intended for tank sizes marked by the weight, and will not work for larger propane tanks measured by their total gallon capacity. For more information on how long a propane tank can last, check out my article “How Long Does A Propane Tank Last? (And How to Check How Full It Is)“.
Propane Appliance Running Time Calculator
20lb Propane Tanks Only Filled to 15 Lbs
As I mentioned at the beginning of this article, both Blue Rhino and Amerigas only fill their propane tanks to 15 lbs of propane, even though the legal limit allows them to be filled to ~20 lbs. While most propane suppliers only fill to 17-19 lbs, Blue Rhino and Amerigas go even further only filling your propane tank to roughly 66% of its total capacity.
The reason Blue Rhino gives for this is that in 2002 when the OPD valve was introduced, which reduced the capacity of the tank by 20% for safety reasons, Blue Rhino reduced the amount of propane they filled tanks to only 17 lbs. And then during the 2008 financial crisis, the prices of propane, steel, diesel fuel, and plastic all rose sharply and in order for them to offer the same product at the same price, they had to reduce the amount of propane in their tanks to only 15 lbs.
However, even after all this time, and including price increases on their end, they still only fill their propane tanks to 15 lbs, even though they can legally fill the tanks to ~20 lbs. So with this in mind, be aware that when you are exchanging a propane tank you may not be getting the full amount of propane your tank can legally hold.
To ensure you are receiving the maximum amount of propane for the best price, it is always recommended to have your tank refilled as opposed to exchanged. Refilling is cheaper per gallon, and you also receive more fuel allowing your propane tank to last much longer between fills.
