1999 mercury tracer rotors?

I went to an auto part store , to buy rotors/disc for my 1999 mercury tracer , guy pulled 2 options , 9 1/4 in diamater or the 10 inch rotors , I went outside and measured my discs , and some what measure 10 inches . not close to 9 1/4 . so i told him . happens he does not have none in stock nor can he order any . so i called same autopart store different location , and they said they had them in stock ,, heres the catch , different measurments. here they are , they have a 9 1/4 and a 10 1/4 i don't know what to buy .. help !!!!!!
1999 mercury tracer rotors?
Buy the big ones. Save your receipt, if they are for some reason incorrect, they will most likely not hassle you on the exchange. A quick call to Ford should yield the correct measurements.