Mango is considered one of the most important fruit crops in Egypt due to its widespread cultivation compared to other fruit crops and in addition to its importance as an important fruit crop it comes in third place after both citrus, oranges, grapes in terms of its contribution to the monetary value of the total Egyptian agricultural exports, and can be crystallized the problem of studying in the possibility of answering questions about what is the concept of the optimal economic size of the farm? What are the factors affecting farm sizes? What are the different measures of farm sizes? What is the optimal economic size of mango farms in new and old lands? To what extent is there a moral impact on the productive efficiency of the farm in question? The research aims generally to measure the optimal size of mango farms in new and old lands and estimate the production functions to identify the value of the marginal output of the various factors of production and estimated the total productivity flexibility of the function by about 1.07 this indicates that the increase of these production elements by the estimated function of 10% leads to an increase in the total output of the acre of mango by about 10.7 % which means an increase in the yield of capacity. The marginal output and average output per productive component were derived from the total output function of the study sample as table (1) showed that the (M.P) for both human labor and nitrogen fertilizer was estimated at about 0.018, 0.029 tons for those productive elements on The order as estimated the value of the marginal product of these productive elements about 210.42, 339.01 pounds respectively.