I am not sure exactly what you are asking but in general the rule is that the carbs be 10% of the calorie intake for the day. It is better to give wet vs. dry. It is also handy to have some higher carb food around for hypo or low numbers that you are trying to steer (which most times includes some type of gravy or sauce).
Have you checked out the following list done by Dr. Pierson? It can help you find the required lower carb food or confirm if you selected food is low carb.
http://catinfo.org/docs/CatFoodProteinFatCarbPhosphorusChart.pdf