Ra VS Grit Size Chart Stainless Steel Surface Roughness Ra to Grit Size Conversion Table

Here is a concise summary table for converting between stainless steel surface roughness (Ra) and abrasive grit size (mesh/grade).

Ra (µm)	Ra (µin)	Equivalent Grit Size (Mesh)	Typical Surface Appearance & Application
3.2	125	40 – 60 grit	Rough, non-reflective; industrial machining marks, non-critical surfaces.
1.6	63	80 – 100 grit	Uniform matte finish; visible abrasive lines, general engineering parts.
0.8	32	180 – 200 grit	Fine matte to semi-gloss; standard brushed finish (e.g., No. 4 finish), smooth to touch.
0.4	16	240 – 320 grit	Low gloss, near-polished; very fine scratches barely visible, pre-polishing stage.
0.2	8	400 – 600 grit	Bright, reflective polish; fine hairline scratches, cosmetic/decorative surfaces.
0.1	4	800 grit	High gloss, mirror-like; scratches almost invisible, optical or medical components.
0.05	2	1200 grit & above	True mirror finish; scratch-free under normal light, high-precision applications.

Range, not exact: The relationship between Ra and grit size is empirical, not a strict mathematical conversion. Actual results depend on pressure, speed, workpiece material, and prior finishing steps.
Higher grit = Lower Ra: Finer grit (higher number) produces a smoother surface (lower Ra value).
Progressive polishing required: To achieve Ra 0.4 or finer, you must start with coarse grit and step through intermediate grits (e.g., 120 → 240 → 400 → 600). Skipping grits leaves deep scratches that finer grits cannot remove.
Typical applications for common values:
- Ra 0.8 (200 grit): Food equipment, architectural panels, standard industrial components.
- Ra 0.4 (240-320 grit): Pharmaceutical vessels, dairy piping, semi-polished molds.
- Ra 0.1 (800 grit): Semiconductor parts, medical implants, high-end decorative trim.