Many people think of glass as a fragile product like the glass that broke in your picture frame. Here is a great visual to show the strength of tempered glass. This is a 3/8″ clear tempered glass shower door with four members of our installation team standing on it. It will bow, but not break! Technically speaking, tempered glass has a minimum surface compression of 10,000 pounds-per-square-inch (psi) and minimum edge compression of 9,700 psi, according to ASTM C1048. That makes it about four times stronger than annealed glass.