It probably goes without saying, but a 100 lb propane tank is designed to hold 100 pounds of propane. Because propane is stored and delivered as a liquid, it can be helpful to know what this looks like in terms of gallons. While there’s a fairly simple answer, there are a few different factors that can affect how many gallons are in a 100 pound propane tank.
The Simple Answer
To put it simply, there are 0.236 gallons per pound of propane (at 60°F).
So, 0.236 gallons x 100 pounds = 23.6 gallons
A 100 lb tanks contains 23.6 gallons
Additional factors don’t add a significant difference to the total volume of 100 pounds of propane, but are interesting to consider.
Each gas cylinder will have a water capacity number stamped on the collar (it will be something like WC 240). This is the total mass of liquid, stated in pounds, that a cylinder could hold if filled entirely with water.
However, when filled with propane, gas cylinders can only be filled up to 42% of the water capacity (this is to accommodate for the fluctuations in tank pressure as temperatures change)
For this example, 240 (water capacity) x 0.42 (max. capacity)= 100.8 pounds
So our tank can actually hold a maximum of 100.8 lb.
As stated above, we know that each pound of propane is 0.236 gallons.
0.236 gallons x 100.8 pounds = 23.789 gallons
Again, this doesn’t make a huge difference, but is still a factor to consider.
How Temperature Affects Tank Pressure
The examples above assume an ambient temperature of 60°F. At this temp, a “full” tank would produce a reading of about 40% on a tank gauge. When temperatures drop, however, that reading will go down. This is not because there is less usable propane in the tank, the propane has just become more dense or compact and the volume has decreased. The reverse happens as temperatures rise; the tank gauge reading will go up, but it’s still the same weight of propane in the tank– the molecules have just become more spread out.
What Happens When Tanks Get Cold?
While there is still the same usable amount of propane in a cold tank, the lower pressure can cause tanks to stop working properly. Keeping tank pressure up may require more frequent refills; even when there is still “usable” propane in the tank, the volume is not high enough and additional propane must be added to bring tank pressure back up.
Heated propane tank wraps can keep you from having to make time consuming and expensive refills by raising your tank temperature and, consequently, your tank pressure. If you frequently use propane during cold weather months, they’re definitely worth checking out! (Give us a call at 888.316.6324 if you have any questions!)