Estimation of development cost, effort and time is difficult and a key problem of software engineering in the early stage of software development. These are estimated by using the function point which is measured from a requirement specification. However, it is often a serious Question of the staffing level required for the software development. The purpose of this paper is to show us the model which can be used to estimate a size of development team. Three hundred one software projects have been analyzed and studied for the model. First, an analysis was conducted for statistical algorithmic model. After various data transformation and regression analysis, it was concluded that no good model was available. Therefore, non-algorithmic model was suggested for analysis, which has random distribution of residuals and makes good performance using RBF (Radial Basis Function) network. Since the model provides a standard to determine the required size of development team, it ran be used as management information.