The radios of particles in Dissipative Particle Dynamics (DPD) method is investigated numerically taking into account size and type of conservative force. In the most of previous studies, the DPD particles have been considered as a point center of repulsion with zero radios and hence sphere size is prescribed by the creation of a structure of frozen DPD particles. Although only in ideal gas state or zero conservative force the DPD point particle is meaningful and with conservative force the DPD particles have an intrinsic size which is assigned by the spherical impenetrable domain occupied by each particle when immersed in a sea of other particles. At first the appropriate method should be define to calculate the size of DPD particle. Different methods including Stokes-Einstein relation, Stokes law and radial distribution function (RDF) are studied and it is concluded that according to limitation of Stokes-Einstein and Stokes relations the RDF is the best method for evaluation of DPD particle size. In the following, the trend of DPD particle size changing and their distribution in the system with linear and exponential conservative force examined. At the end we demonstrate that the employing of exponential conservative forces for the colloid-colloid and colloid-solvent interactions but keep the conventional linear force for the solvent-solvent interactions achieve a well-dispersed suspension with different particle sizes without extra computation