The average compressed air tank has a pressure rating of 3000 PSI (pounds per square inch). Smaller tanks can have ratings as low as 1800 PSI while larger ones can have ratings as high as 4500 PSI.  The size of the tank will determine how many shots can be fired before it needs to be refilled. Smaller tanks are able to hold less gas, meaning fewer shots, while larger tanks are able to hold more gas, meaning more shots.