Tolerances are an important part of production where the desire to produce quality products have to be weighed against the increased production costs. The desired tolerance will influence the choice of both production method as well as the machine used. Given that machining is an adequate production method, variation of the required surface roughness will imply a variation of the part cost which needs to be taken into account during production planning. This paper presents a method for evaluating the tolerance cost in regards to surface roughness during longitudinal turning operations, thus enabling a better comparison between different production situations.