The design of the body shape of spur gears has an effect on the deformation and thus also the stiffness of the gearing. The stiffness of the gearing is a parameter that significantly affects the noise level of transmission mechanisms. Determining the gear stiffness is difficult due to the shape of the gear teeth. The paper examines the influence of the shape and size of individual gear body parameters on gear deformation. Deformation is solved by finite element method. On the basis of the deformation of the gearing, the stiffness of the gearing is determined.