Surface Roughness Calculator (Ra / Rz)
Convert surface roughness between Ra, Rz, Rq, and Rt in micrometers.
Returns ISO 1302 finish grade (N1-N12), machining process, and suitable applications.
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.