Comments in regards to this complaint are correct to some degree. Propane weight can vary even though it is said that propane weighs 4.2 lbs, this weight is based on industry stated average. The so called "domestic household" propane has a specific gravity range of liquid anywhere from the average of 0.505 to 0.514 sg and the gas composition can varied which can cause the weight per gallon to vary roughly anywhere from 4.2 to 4.3 lbs per gallon. Each loads of propane comes from different sources throughout the country can vary, so unless you can validate the weight of propane by some "approved" means, you're playing a guessing game. Generally as a rule of thumb you subtract 42% (providing you're in the specific gravity range .505 to .514), from the water capacity of the cylinder For example, if the "WC" stamped on the cylinder states "45" this means cylinder capacity is 45 lbs of water that it can hold, therefore as a general rule of thumb 45 lbs x 42% = 18.9 lbs of propane the cylinder can hold, so if the weight of propane is 4.24 lbs per gallon, this means it can hold roughly 18.9/4.24 = 4.5 gallons of propane.