Surface Finish Ra/Rz Converter

Inputs

Known value Choose the surface-finish value you have.

Roughness value Known Ra, Rz or RMS value.

µm

ISO N grade (N) Nominal ISO roughness grade N1 through N12.

Results

Default result

Ra

1.6µm

Also computed

Rz6.4µm

Approximate; process-dependent.

RMS1.776µm

ISO N gradePass7

Within the N1–N12 nominal grade range.

Method notes 2 notes

Approximate machining conversions: RMS ≈ 1.11·Ra and Rz ≈ 4·Ra. Real Rz/Ra varies with process and surface profile shape.
ISO N grade nominal roughness uses Ra(µm) = 0.0125 · 2^N, so N7 corresponds to Ra 1.6 µm.

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