I need to know how many gallons of propane my tanks can hold?

My house is heated with propane. I have 2 tanks outside that are ROUGHLY 44" tall and 27" in diameter. I used a tape measure and was eyeballing it while standing in 3' of snow, so give or take a few inches on the size. I need to know how many gallons of propane each tank could hold and what is considered full. I think I am getting hosed by my fuel company. Thank you for any help