A 3D simulation technique to estimate density of particulate matter (PM) from spark ignition (SI) gasoline engines is proposed. The technique is based on a two-equation model consisting of coupled conservation equations of soot particle number and mass and fluid transportation equations.The nucleation rate of soot particles was obtained from a database built by simulation of elementary reaction with the proposed technique. Two approaches were explored to obtain the nucleation rate. One involves 0-dimensinal SI simulation and the other involves 1-dimensinal flame propagation simulation.The estimation results were verified with measurement data obtained with a single cylinder SI engine a homogeneous pre-mixed fuel was supplied. It was confirmed that appropriate results could be obtained with the 1-dimensional approach for the nucleation rate model.