# Roughness Parameters

## Mean Roughness

The Mean Roughness (Roughness Average Ra) is the arithmetic average of the absolute values of the roughness profile ordinates. Ra is one of the most effective surface roughness measures commonly adopted in general engineering practice. It gives a good general description of the height variations in the surface. The units of Ra are micrometres or microinches.

Note: Ra is also called AA and CLA. Z(x) = profile ordinates of roughness profile

## Root Mean Square (RMS) roughness (Rq)

The Root Mean Square (RMS) roughness (Rq) is the root mean square average of the roughness profile ordinates.

Note: Rq is also called RMS. ## Roughness Depth

The Single Roughness Depth (Rzi) is the vertical distance between the highest peak and the deepest valley within a sampling length.

The Mean Roughness Depth (Rz) is the arithmetic mean value of the single roughness depths of consecutive sampling lengths.

The Maximum Roughness Depth (Rmax) is the largest single roughness depth within the evaluation length.

The units of Rz are micrometres or microinches. ## Roughness Profile Slope

The Mean width of profile elements (RSm) is the arithmetic mean value of the widths of the profile elements of the roughness profile, where a profile element is a peak and valley in the roughness profile. The units of Rsm are micrometres or microinches.

The Root Mean Square Slope (Rsq) is the root mean square average of all local profile slopes. Each slope is calculated using a smoothing algorithm to reduce the effect of random noise on the valjue of Rsq. 