Curve sawing is a standard method to handle break-down of crooked logs at sawmills and means advantages for yield and quality of sawn boards. However, for circular saw machinery and especially for double arbor saw machinery, deviations of saw kerfs give losses of valuable board volume. Saw kerf deviations give thinner boards compared to straight sawn boards but also slight cupping of the cross sections. Theoretical calculations show that even with the moderate (large) curve radii that is used today in sawmills with circular saw machinery, these saw kerf deviations are typically 0.2-0.6 mm for normal saw machinery and Swedish log material.The test sawing reported here was made in order to give experimental values that can be compared to theoretical values. 50 normal logs and 50 curved with top diameter 236-248 mm were cut with sawing pattern 3X with center boards 51x149 mm. The average curve radius of the curved cants that were cut in the resaw was 132 m (bow height 19 mm) and the theoretical saw kerf deviation for this radius is 0.31 mm. The experimental results show that the thickness reduction at the measuring points for curve sawn boards compared to straight sawn boards was in average 0.19 mm to be compared with the theoretical value of 0.20 mm. Cupping was more difficult to measure but results seem to agree well between theory and experiments.