The BTU of the burner determines how long your propane fire pit can burn. A 20lb (4.7 gallon) tank holds roughly 430,000 BTU of gas and can last 4 to 4 1/2 hours with moderate gas output. At an average price of $3.25 a gallon, you could easily spend an hour with your family around the fire for less than $3. That's my kind of low-cost entertainment!