Marginal product of an input (factor of production) is the extra output that can be produced by usingone more unit of the input (for instance, the difference in output when a firm's labour usage is increasedfrom five to six units), assuming that the quantities of no other inputs to production change. Marginalproduct, which occasionally goes by the alias marginal physical product (MPP) is the one of the twomeasures derived from the total product. The other is average product. Marginal product is directlyproportional to total product.