Gray cast iron is widely used in several applications that require combination between low roughness Ra values and narrow dimensional tolerances. Therefore, grinding can be an alternative process to be used at the end of the production chain for manufacturing products having such requirements. Furthermore, to determine metrological traceability and improve reliability of measurements of surface roughness values, that allows to take best decisions, the comparison of the results obtained with other reference values are indispensable. This can be performed through the calculation of measurement uncertainty. Into this context, calculation of the measurement uncertainty associated with the surface roughness Ra parameter of FC 250 Gy cast iron after the grinding process was performed. Different cutting conditions were used (cutting speed (Vc) = 31.16 m/s, workspeed (Vw) = 7.5 m/min, number of passes of grinding wheel on the material surface (1 and 2) and radial depth of cut (ae) = 15 µm and 30 µm) and silicon carbide grinding wheel and under a coolant environment. The roughness Ra was measured on the ground surface of the workpiece and the measurement uncertainty was calculated by the GUM method. The results showed that the reduction in the number of passes together with the increase in the radial depth of cut resulted in the highest roughness Ra value of 0.78 µm. The measurement uncertainty was calculated for the two conditions: two passes of 15 µm and one pass of 30 µm, resulting in Ra = (0.73 ± 0.08) µm and Ra = (0.78 ± 0.06) µm, respectively. The variability of the readings was the greatest contribution to the final measurement uncertainty associated with the obtained Ra (by about 87.06% and 71.69% for two passes of 15 µm and one pass of 30 µm, respectively). Also, Ra surface roughness increased with radial depth of cut.