Enter the average roughness and the maximum roughness depth into the calculator to determine the surface roughness; this calculator can also evaluate any of the variables given the others are known.

Surface Roughness Formula

The following formula is used to calculate the surface roughness:

SR = (Ra + Rz) / 2


  • SR is the surface roughness
  • Ra is the average roughness
  • Rz is the maximum roughness depth

To calculate the surface roughness, add the average roughness and the maximum roughness depth, then divide the sum by 2.

What is a Surface Roughness?

Surface roughness, also known as surface texture, is a measure of the texture and roughness of a given surface. It is a critical aspect in many manufacturing processes and has significant implications on the performance, appearance, and wear resistance of a product or component. Surface roughness is typically quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth. These deviations can be due to a variety of factors, including the material properties, the type of manufacturing process used, and the environmental conditions during manufacturing. Surface roughness can be measured using a variety of techniques, including contact methods (such as stylus profilometers) and non-contact methods (such as optical profilometers and interferometers).

How to Calculate Surface Roughness?

The following steps outline how to calculate the Surface Roughness:

  1. First, measure the surface profile using a suitable instrument.
  2. Next, calculate the average roughness (Ra) by finding the arithmetic mean of the absolute values of the profile deviations from the mean line.
  3. Next, calculate the root mean square roughness (Rq) by finding the square root of the average of the squares of the profile deviations from the mean line.
  4. Finally, calculate the maximum roughness (Rmax) by finding the maximum peak-to-valley height within the measured profile.
  5. After performing the calculations, compare the results with the specified surface roughness requirements.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Measured surface profile: [2, 4, 1, -3, 0, 5, -2, 1]

Calculate the average roughness (Ra), root mean square roughness (Rq), and maximum roughness (Rmax).