That is after you take out the moisture component of the food.
Here is a link. It isn't totally accurate using the min/max values but it can help guide you.
Also Dr. Lisa list is a good resource as well.
https://catinfo.org/docs/CatFoodProteinFatCarbPhosphorusChart.pdf You can read a bunch of additional notes at the end. They can be very helpful in helping in determining a good food to try.
Remember though...the best food is the one he will eat! Even if it means a higher carb one till you can find something in the lower carb range he will eat.