Engineering · Calculator
Surface finish converter.
Ra ↔ Rz ↔ RMS ↔ CLA — convert between the four most-cited surface roughness scales. Quick conversion for the common case where a drawing cites one scale and your inspection equipment reads another.
Enter any value, see the others
Roughness conversion.
Conversion factors: 1 µm = 39.37 µin · Rz ≈ 4× Ra (typical for machined surfaces, varies by process) · RMS ≈ 1.11× Ra · CLA ≡ Ra (legacy term).
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What surface finish each process delivers.
| Process | Ra (µin) | Ra (µm) |
|---|---|---|
| Rough turning / milling | 125–500 | 3.2–12.5 |
| Standard turning / milling | 63–125 | 1.6–3.2 |
| Finish turning / milling | 32–63 | 0.8–1.6 |
| Precision milling | 16–32 | 0.4–0.8 |
| Reaming | 32–63 | 0.8–1.6 |
| Wire EDM (rough) | 64 | 1.6 |
| Wire EDM (single skim) | 16 | 0.4 |
| Wire EDM (double skim) | 8 | 0.2 |
| Wire EDM (4-pass skim) | 4 | 0.1 |
| Cylindrical grinding | 8–32 | 0.2–0.8 |
| Surface grinding | 8–32 | 0.2–0.8 |
| Honing | 4–16 | 0.1–0.4 |
| Lapping | 0.5–4 | 0.012–0.1 |
| Polishing | 1–8 | 0.025–0.2 |
| Electropolishing | 4–16 | 0.1–0.4 |
Keep exploring
Related tools & references
Typical Ra by process and what each finish looks like.
Finish-pass feeds that drive the Ra you can hold.
Pair surface finish callouts with dimensional tolerances.
How tighter finish and tolerance callouts raise cost.
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