Filtration is a necessary step in roundness measurement. The type of filter affects value of roundness error. There were many studies that explain the differences between filters theoretically and few of them have studied the differences practically. This study aims at introducing a practical comparison of the following filters (2CR50, 2CR75, 2CRPC50, 2CRPC75, Gaussian and no filter) in order to demonstrate the effect of each on roundness error values. RA-120 ROUNDTEST instrument was used for measuring out of roundness of 25 turned workpieces. Least squares reference circle (LSC), minimum zone reference circle (MZC), maximum inscribed reference circle (MIC) and minimum circumscribed reference circle (MCC) methods were used for out of roundness evaluation. The experimental study showed that the filters have a clear effect on the values of the roundness error (RONt) and 2CRPC50, 2CR50 and Gaussian filters give the lowest values of (RONt) compared to others and the relationship between them depends on relation between a sinusoidal wavelength λ and the cut-off in length λc . Also from ANOVA analysis the method (LSC, MZC, MIC and MCC) used in RONt evaluation does not affect the relationship between the above-mentioned filters, but rather affects their values