# 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.