Rhonda,
  That varies depending upon age and breed. Typically urine pH target
is 6.2-6.4 for a normal healthy adult cat. As cats grow older the risks
change. While younger cats are more inclined toward struvite crystal
formation which can be helped by keeping urine pH between 6.2-6.4,
older cats are more at risk for Calcium Oxalate crystals and stones
which can best be helped by urine pH a bit less acidic at 6.4-6.6.
   Breed issues enter the picture because some breeds are more prone
to calcium oxalate formation as well. Persians, Himalayan and Burmese
appear to be more prone to CaOx stone formation.