The average gas fire pit will last from 3 to 6 hours on a 20 lb. propane tank.  Depending on your fire pit BTU rating a tank can last you as long as 9 hours, or as little as 1-1/2 hours.  A 20 pound propane tank contains approximately 430,000 BTU’s.  To determine how long the tank will last with your fire pit divide 430,000 by the BTU rating of your fire pit. Below we have a table where you can determine how long your gas fire pit will last on a 20 pound propane tank.