Exhaust help

Does any one know the exact measurement of the exhaust piping on the v6 3400 alero, im cutting out my cat and putting a high-flow one on but the cats size is just alittle to big and i need to know the exact measurement so i can get the right reducers. i want to go with 2.00'' but im not for sure, im also cutting out my resinator and putting in a piece of straight up which is another reason i need to know the measurement thanx and i hope some one can help.