Carbs = 100 – (crude protein + crude fat + moisture + crude fiber + crude ash)
AAFCO labeling conventions do not require the carb content to be shown in the guaranteed analysis on the label of cat food. If you want to determine the carbohydrate content of cat food you need to do it by yourself. You can find out the carb content of cat dry foods by adding up the percentage of crude protein, fat, moisture, fiber, and ash from the guaranteed analysis, and then you have to subtract their sum from the total of 100%.