Yes, c5 rotors are 12.8", but rounding up to 13" is so much easier to say. Haha.
Mine: 1998 Trans Am - 6.0L and T56 swap, C6 brakes, nitrous, not slow
Brother 1: 1998 Grand Prix GT 2-door - 3.8L SC and 5-spd manual swap coming soon
Brother 2: 2000 Grand Prix GTP 4-door - stock until he learns to stop breaking his junk.