Surface finish Ra and Rz Roughness Specification

 Roughness Average -Ra

Ra is the arithmetic average of the absolute values of the profile heights over the evaluation length.

Ra surface roughness

 Ten Point Height of Irregularities – Rz(ISO) 

RZ is the average value of the absolute values of the heights of five highest-profile peaks and the depths of five deepest alleys within the evaluation length.

Surface roughness terminology and parameters

Rz surface roughness

Ra and Rz are different parameters of roughness.

  • Ra is the average roughness of a surface.
  • Rz is the difference between the tallest “peak” and the deepest “valley” in the surface.

Ra vs Rz is like comparing inches to meters. They are not compatible. Use one or the other not both.

Surface roughness technical data