Deformation Length is one of the most important parameters in cold roll-forming process, which plays a fundamental role in determining the inter-distance between the stations and rate of deformation. Deformation length was first introduced by Bhattacharyya. He also obtained a closed-form relation for this length in roll-forming of symmetric channel section. In this paper, deformation length in the roll forming of the circular cross section is examined and determined. To do this, analytical method and finite element simulation are used. The analytical method presented in this paper is based on the approach of Bhattacharya's suggestion. Due to the fact that the deformed sheet geometry is more complex, hence the related equations of strain and deformation energy would become more complex too, and therefore analytical solution is going to be more difficult compared to symmetric channel section. Using the present analytical method, deformation length is computed for a specific numerical case study and the analytical results are compared with the results of finite element simulation of the ABAQUS commercial software. Correlation between the analytical and finite element simulation results demonstrates the validity of the presented analytical method. In the end, the effects of forming parameters on the deformation length are studied.