Estimation of the draft requirement of tillage implements is important from machine design, and tractor selection viewpoints. In this study, a model was developed to calculate the draft force and power of a disk plow. In this model, the effects of soil cutting, soil displacement, and soil-metal friction processes on the specific draft force of a disk plow were considered. Model inputs consisted of the soil parameters, the plow parameters, and the working condition parameters. To simplify the required calculations, the derived equations were entered in the Excel software, and the finalized spreadsheet was utilized as the disk plow draft force and power calculator. One of the advantages of the developed model was that the required calculations did not depend upon the dimensionless N-factors. Model verification was carried out by comparing the model outputs with the corresponding results of other studies. Moreover, the output of the model and the measured draft force of plowing on a silty clay loam soil were compared. According to the results of this study, the form of equation developed in this paper and the Hendrick's formula regarding the specific draft force, were compatible, since both equations were polynomials of order 2 with respect to the forward velocity of the plow. On the other hand, the developed model overestimated the required draft force of a disk blade in comparison with the Godwin's model; however, the average value of overestimation was only 18%. Moreover, draft force and power requirements of a three-blade disk plow working on a silty clay loam soil with the forward velocity of 7 km h(-1), were 11.3 kN, and 22 kW, respectively, that were about 5% lower than the results obtained by the developed model (11.8 kN, and 22.95 kW). Therefore, the developed model can be used to calculate the disk plow draft force and power with reasonable accuracy. (C) 2016 Elsevier B.V. All rights reserved.