I would feed a snake that size a weanling mouse weighing about 15 grams-17 grams. I gradually increase the mouse size as the snake approaches 200 grams, and by the time they are 200 grams they are eating small adult mice of about 17-21 grams. When they are up over 250, then they get mice that are about 25 grams. I don't feed jumbo mice, 28 grams or bigger, to anything but the largest corns, that are eating bi-weekly.
Looking at that advice, it seems like the mouse weight is about 10% of the snake weight. That really only holds true for just this very narrow weight range of 150-250 gram corns.