Rmax Surface Finish Definition

The smooth or rough texture of a surface can be measured and quantified to better regulate its manufacturing process.


A more textured surface has a higher maximum roughness, or Rmax.A more textured surface has a higher maximum roughness, or Rmax.
Rmax is one of many methods available for measuring the roughness of a surface.

Rmax is the measure of maximum roughness. It is the distance, in height, measured from the top of the highest peak to the bottom of the lowest valley of a surface texture. Rmax is measured in either microinches (one-millionth of an inch ) or microns (micrometers, or one-millionth of a meter).


Rmax is determined by a profilometer, a hand-held device which measures the physical depth of surface irregularities using a brush or diamond stylus. Since maximum roughness is a measure of the extreme depth, not an average, one deep scratch can greatly affect the Rmax.


There are other methods of measuring roughness, such as Ra, Rz, Rp, Rq, Rx and Ry, though the most common method is Ra or roughness average. Rmax only measures the vertical component, or height, of the surface texture, though other parameters, such as waviness, hybrid and spacing measure the surface in two and three dimensions.

About the Author

Ann Salter began writing professionally in 2010 and has worked extensively in the fields of art, architecture and design since 2004. Her work has appeared in informative guides on student housing cooperatives and sustainable building alternatives. Other areas of specialty include technology, health, gardening and cooking. Salter holds a Bachelor of Architectural Studies from the University of Waterloo.