What is dry matter basis?
Pet foods and animal feeds differ greatly in moisture content — wet food can be 75-80% water while dry kibble is only 10%. To make a fair comparison of nutritional value, you convert the guaranteed analysis percentages to a dry matter basis, which removes the water and shows what % of the actual food solids is a given nutrient.
Formula
Dry Matter % = Nutrient % / (100 - Moisture %)