Convert between Ra, Rz, RMS, and CLA surface finish measurements in microinches and micrometers. Includes common reference finishes for mill, ground, lapped, and polished surfaces.
Last updated April 2026
| Finish | Ra (uin) | Ra (um) | Description |
|---|---|---|---|
| As-cast / Flame cut | 500 | 12.5 | Rough industrial surfaces |
| Sawing | 250 | 6.3 | Bandsaw or circular saw cut |
| Rough machining | 125 | 3.2 | Heavy milling or turning |
| Standard machining | 63 | 1.6 | General-purpose CNC finish |
| Fine machining | 32 | 0.8 | Finish pass milling or turning |
| Grinding | 16 | 0.4 | Surface or cylindrical grinding |
| Honing | 8 | 0.2 | Precision honing |
| Lapping | 4 | 0.1 | Precision lapping |
| Superfinishing | 2 | 0.05 | Mirror-quality surface |
Ra (arithmetic average roughness) is the most common surface finish measurement. It represents the average deviation of the surface profile from the mean line, measured in microinches (uin) or micrometers (um).
Standard CNC machining produces Ra 63 uin (1.6 um). Fine machining achieves Ra 32 uin (0.8 um). Ground surfaces are typically Ra 16 uin (0.4 um). Lapped surfaces reach Ra 4 uin (0.1 um).