One of two terms will tell you the wall thickness of your pipe, either the "Schedule" or "Gauge." If you are using true IPS sizes, the wall thickness is determined by the schedule - the higher the schedule, the thicker the wall, i.e. 1-1/2" schedule 80 has a thicker wall than 1-1/2" schedule 40. For gauge sizes, the lower the number, the thicker the wall, i.e. 1.90" diameter 11 gauge is thicker than 1.90" diameter 12 gauge.