The present study investigates the effects of cutting parameters (cutting speed, feed rate, and depth of cut) on the roughness of the finished surface during turning C45 steel using CNC QUICK TURN 150 SG (Mazak, Japan) with carbide inserts WNMG431PP CA525 (Kyocera Precision Tools TAC08616). The experiment design was based on the Taguchi method. The results show that the feed rate significantly influences surface roughness; the cutting velocity is second in order, and the depth of cut is the weakest influence parameter on the surface roughness. The regression equation was proposed to predict the roughness of turned surfaces and its determination coefficient ( ) of 0.9985. The prediction predicted by the regression models is compared to the experiment. The mean absolute and square error values are 6.73% and 0.85%. Hence, the model is reliable in estimating surface roughness.