Surface Roughness Calculator (Ra / Rz)
Convert between Ra, Rz, and Rq surface roughness values.
Includes ISO finish grades and machining process guidance.
Surface Roughness
Ra (Arithmetic Mean Roughness) Ra is the average absolute deviation of surface heights from the mean line. It is the most widely used roughness parameter worldwide.
Rz (Mean Roughness Depth) Rz ≈ 4 × Ra for typical machined surfaces. Rz measures the average peak-to-valley height over five sampling lengths.
Rq (Root Mean Square Roughness) Rq ≈ 1.11 × Ra. Also known as RMS roughness — commonly used in optics and precision metrology.
ISO Finish Grades (N-series) N1 (Ra 0.025 µm) through N12 (Ra 50 µm). Each step doubles the Ra value — a geometric series.