Surface Roughness — Glossary Entry

Surface Roughness is the arithmetic average of the absolute deviations of the surface profile from the mean, expressed in micrometres (µm) and denoted Ra. A lower Ra means a smoother surface.

Typical Ra by application

• Precision slitter (film, foil): Ra ≤ 0.2 µm
• Standard slitter (paper): Ra ≤ 0.4 µm
• Tissue slitter: Ra ≤ 0.4 µm
• Granulator: Ra ≤ 0.8 µm (less critical)
• Plate shear: Ra ≤ 0.4 µm on the cutting face

How to measure

• Contact profilometer: most accurate, trace over 4–12 mm
• Optical profilometer: non-contact, suitable for soft coatings
• Stylus profilometer: classic, contact-based
• Compare to a calibrated roughness specimen for spot checks

See also.