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Surface Roughness.
Convert between Ra (Arithmetic Average), RMS (Root Mean Square), and Rz (Average Maximum Height) surface finish specifications.
Equivalents
Ra (µm)
RMS (µin)
Rz (µm)
The Mathematics
These conversions are approximations based on typical machining profiles. Actual ratios vary based on the specific machining process (turning vs grinding).
Standard Approximations
Ra (µm) ≈ Ra (µin) / 39.37
RMS (µin) ≈ Ra (µin) × 1.11
Rz (µm) ≈ Ra (µm) × 4 to 7 (We use 4.0 for standard turning/milling)