Complete comparison of surface finish parameters: Ra vs Rz vs RMS. Charts, equivalents, and how to specify finishes for machined parts.
Surface finish quantifies the texture of a machined surface.
The arithmetic average of absolute profile heights. Most commonly used. Values range from 0.025 μm (mirror) to 25 μm (rough saw cut).
Average of five highest peaks and five lowest valleys. Rz = 4-6x Ra typically. Better at detecting isolated defects.
Squares values before averaging. RMS ≈ 1.1x Ra for typical isotropic surfaces.
| Ra (μm) | Ra (μin) | Description |
|---|---|---|
| 0.025 | 1 | Mirror — laps, diamond turning |
| 0.05 | 2 | Optical — precision ground |
| 0.1 | 4 | Very fine — honed |
| 0.2 | 8 | Fine — precision machining |
| 0.8 | 32 | Standard machining finish |
| 1.6 | 63 | Medium machining |
| 3.2 | 125 | Coarse machining |
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