The development of a calculation approach to determine the Percentage Depth Dose (PDD) by manual calculation for medical linear accelerator of 6 MV and 15 MV photon beam energy. The equation to determine PDD can be divided into two components i.e., the primary component and the scatter component. To calculate the primary component, the linear attenuation coefficient needs to be calculated. The measurement of charge was taken at various depths and for different field sizes using 6 MV and 15 MV photon beams. To determine the linear attenuation coefficient, a graph of ln (MR) where, MR represents corrected meter reading was plotted against depth in cm. By plotting another graph of linear attenuation coefficient against field size, to determine the effective linear attenuation coefficient. The scattered component KS was graphically plotted against depth in cm and derived an equation for scatter component. The calculated PDD for 6 MV was found to be within 1 % difference and for 15 MV percentage difference within 3 %. It was found that numerically developed PDD values table for higher energy photon beam becomes valid and it can be utilized for the manual dose calculation.