Exhaust pipe sizes

[rock883]

Hey there, I have a glasspack on my explorer (CRAP) and I am thinking about getting a flowmaster delta flow 40 series muffler and I was just going to cut the pipe and the front and back of the glasspack and then slip the flowmaster in and crimp it on, but I need to know what size the pipe is?? I had the guy put in the same type of pipe as stock, so it should be the same size. Thanks