Precision feeding reduces costs, increases sustainability, and may improve traceability. In young pigs, feed intake increases exceeds nutrient requirement increases, and it is beneficial to use a high nutrient diet. Later, nutrient requirement is less and grower pigs can be fed a less nutrient dense diet. The use of multi-phase diets is already well established, but it does  not address individual variation within a production stage. The nutritional requirement of an individual is hard to determine due to the normal (curvilinear) distribution of nutrient requirement in a population, so a new method was designed in this study. The “grey-box” method is based on individual body weight, growth, and feed intake patterns.  After creating a mathematical model, calibration trials were run. The first calibration trial was to determine individual lysine requirements, and the second trial validated the mechanistic component. Validation trials were then run, and showed the determined lysine requirement was accurate and nitrogen loss reduced. Using the system designed, it was calculated 8% on feed costs was saved, and that it could provide a more sustainable farming technique.