X-Ray diffraction is a tool for the investigation of the fine structure of matter. Initially X-Ray diffraction was used only for the determination of crystal structure but now a days the data from X-ray diffraction have also been  used to determine the crystalline size using Debye-Scherrer formula.  Generally one has to deal with limited data because of laborious and time consuming manual methods of calculation. Sometime calculations with lots of data are required in order to determine different crystalline sizes for the statistical analysis or other applications. To overcome the difficulties of dealing with large data, a computer programme in VB. NET has been developed to calculate crystalline size using Debye-Scherrer formula. Use of this software (Computer programme), the calculations of crystalline size is saves lots of labour and time. This software can be a very handy tool in the field of Material Science, especially in Crystallography, etc. the software can easily be developed in “C” however, to make the software more user friendly, faster and easier to handle, the VB.NET has been used here.