The "choke" is figured on how much the barrel is constricted down from the "cylander" measurement. You cannot just measure the muzzle of the shotgun and determine the actual "choke". Choke guages have legs on them to measure inside diameter down the barrel in front of the choke constriction. A second measurement is then taken at the muzzle and the two numbers are subtracted. The choke is determined by that derived number. No, I don't have the chart that shows which chokes are which constrictions.
I think I may have found the answer. Thanks to the one who posted this on another thread.