Roughness Calculator
Convert between Rz, Ra and ISO roughness grades (N0 — N12)
ISO Roughness Grades Reference Table
| Grade | Rz max (µm) | Ra max (µm) |
|---|---|---|
| N0 | 0.116 | 0.0125 |
| N1 | 0.217 | 0.025 |
| N2 | 0.406 | 0.05 |
| N3 | 0.758 | 0.1 |
| N4 | 1.415 | 0.2 |
| N5 | 2.643 | 0.4 |
| N6 | 4.935 | 0.8 |
| N7 | 9.215 | 1.6 |
| N8 | 17.206 | 3.2 |
| N9 | 31.675 | 6.3 |
| N10 | 58.722 | 12.5 |
| N11 | 109.648 | 25 |
| N12 | 204.738 | 50 |
What is Ra?
The arithmetic average roughness value Ra describes the arithmetic average of all deviations in the roughness profile from the median line within a measured length. It is the most commonly used roughness parameter in engineering drawings and surface finish specifications.
What is Rz?
Rz (mean roughness depth) is established by dividing the measurement length into five equal segments and calculating the average of the peak-to-valley distances within each segment. It is more sensitive to occasional deep scratches or high peaks than Ra.
Why is there a conversion interval?
A direct 1:1 conversion between Rz and Ra is not possible because different surface profiles can yield the same Ra but different Rz values. The common rule “Rz = 4 × Ra” is a rough approximation. In practice, the ratio typically falls between 4 and 7 depending on the manufacturing process. This calculator uses standard ISO reference values for accurate grade assignment.
Need a Specific Surface Finish?
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