In the pork industry feed is consistently the largest input cost. Within feed, energy is the most expensive ingredient.Therefore it is important to have a consistent and accurate measurement of feed energy for any diet. NE is agreed to be the most accurate measure of dietary energy but complicated to evaluate. NE is defined as the metabolizable energy minus the heat increment. Essentially it is the efficiency of the utilization of metabolizable energy. Since NE measure the amount of energy an animal uses for productive functions (movement, lactation, growth, and gestation) it is considered the ideal energy measure. The paper proposes three ways to determeine NE 1)Comparative slaughter technique measures the energy gained in a carcass over a period of time. 2) Prediction equations are used to estimate NE, this requires specific knowledge of ingredients or digestible nutrients. Most of these equations have been made using a calorimeter, and require that measurements of nutrients be done in  similar way (lab analysis) that the equation was developed. 3) Indirect calorimeter is another way to measure NE which involves using an individual pig air chamber. It is important for producers and feed formulators to have a basic understanding of the derivation of the methods used and why these values may vary depending on the system used.