〰 Surface Finish · ISO 1302 · ASME B46.1

Surface Roughness Converter

Enter any one parameter Ra, Rz, Rq, Rt, or N-grade and get all others instantly. Includes ISO reference table and machining process guide.

Ra / Rz / Rq / Rt N1 – N12 Grade μm & μin ISO 1302 ASME B46.1
ℹ️ Ratios per ISO 4287 / ISO 1302 and ASME B46.1. Rz ≈ 6×Ra, Rq ≈ 1.11×Ra. These are reference approximations measure actual parts with a profilometer for critical work.
〰
Input
μm
Result
N6
General machined surface
Turning, Milling, Boring, Grinding · Ra = 0.8 μm
Ra
μm
Rz
μm
Rq (RMS)
μm
Rt
μm
Ra (μin)
μin
Rz (μin)
μin
Rq (μin)
μin
Rt (μin)
μin
Surface Finish Quality Scale
← Super-finish (N1) (N12) Rough casting →
0.025 μm 0.8 μm 50 μm
Conversion Ratios Used
Rz ≈ 6 × Ra ISO avg. (range 4–7×)
Rq ≈ 1.11 × Ra Root-mean-square factor
Rt ≈ 7.5 × Ra Max profile height approx.
Ra(μin) = Ra(μm) × 39.3701 ASME B46.1
N-grade Ra = 0.025 × 2^(N−1) ISO 1302 each step doubles

ISO 1302 Roughness Reference Table

N-grade to Ra, Rz, Rq, Rt values with machining processes. Highlighted row = closest match to your input.

Grade Ra (μm) Ra (μin) Rz (μm) Rq (μm) Rt (μm) Machining Process

About This Converter

Surface roughness is clearly specified on drawings through Ra value, N-grade, or a finish symbol. But whenever a value needed to be converted from one parameter to another, or Ra had to be derived from an N-grade, it had to be calculated manually.

This converter provides everything in one place: Ra, Rz, Rq, Rt in both μm and μin, plus ISO N-grade, a quality bar, and a reference table with machining processes. No login, no ads, free to use.

Part of TaskJunction free mechanical engineering calculators for Indian engineers and students.

Vaibhav Dhokpande, Mechanical Engineer & Developer, TaskJunction