Surface roughness conversion
Enter an Ra value to get the N grade, the ∇ class found on older drawings, and the machining method that achieves it.
- N grade (ISO 1302)
- N7 (Ra 1.6 μm)
- Ra (μin)
- 63.0 μin
- Estimated Rz
- ≈ 6.4 – 11.2 μm
- ∇ class (GOST, old TCVN)
- ∇6 (Ra 1.25 – 2.5 μm)
- Nearest old JIS mark
- ▽▽▽ (Ra 1.6, 6.3S)
- Typical method
- Finish turning, finish milling, reaming
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📘 Free download: CNC machine buyer's guide 2026 (PDF) →- Rz is only an estimate (typically Rz ≈ 4–7 × Ra depending on the process); if the drawing specifies Rz, use the Rz value. ∇ classes are from older standards (GOST 2789, old TCVN) still seen on older drawings.
Surface roughness conversion chart
Rz is only an estimate (typically Rz ≈ 4–7 × Ra depending on the process); if the drawing specifies Rz, use the Rz value. ∇ classes are from older standards (GOST 2789, old TCVN) still seen on older drawings.
| N grade (ISO 1302) | Ra (μm) | Ra (μin) | Estimated Rz (μm) | ∇ | JIS | Typical method |
|---|---|---|---|---|---|---|
| N12 | 50 | 1968 | ≈ 200.0 – 350.0 | ∇1 | — | Rough turning, rough milling, sawing |
| N11 | 25 | 984 | ≈ 100.0 – 175.0 | ∇2 | ▽ | Rough turning, rough milling, sawing |
| N10 | 12.5 | 492 | ≈ 50.0 – 87.5 | ∇3 | — | Rough turning, rough milling, sawing |
| N9 | 6.3 | 248 | ≈ 25.2 – 44.1 | ∇4 | ▽▽ | Standard turning and milling |
| N8 | 3.2 | 126 | ≈ 12.8 – 22.4 | ∇5 | — | Standard turning and milling |
| N7 | 1.6 | 63 | ≈ 6.4 – 11.2 | ∇6 | ▽▽▽ | Finish turning, finish milling, reaming |
| N6 | 0.8 | 31 | ≈ 3.2 – 5.6 | ∇7 | — | Finish turning, finish milling, reaming |
| N5 | 0.4 | 16 | ≈ 1.6 – 2.8 | ∇8 | — | Grinding, precision turning |
| N4 | 0.2 | 8 | ≈ 0.8 – 1.4 | ∇9 | ▽▽▽▽ | Grinding, precision turning |
| N3 | 0.1 | 4 | ≈ 0.4 – 0.7 | ∇10 | — | Fine grinding, lapping, polishing |
| N2 | 0.05 | 2 | ≈ 0.2 – 0.4 | ∇11 | — | Fine grinding, lapping, polishing |
| N1 | 0.025 | 1 | ≈ 0.1 – 0.2 | ∇12 | — | Fine grinding, lapping, polishing |
| Class ∇ | Ra (μm) |
|---|---|
| ∇1 | 40 – 80 |
| ∇2 | 20 – 40 |
| ∇3 | 10 – 20 |
| ∇4 | 5 – 10 |
| ∇5 | 2.5 – 5 |
| ∇6 | 1.25 – 2.5 |
| ∇7 | 0.63 – 1.25 |
| ∇8 | 0.32 – 0.63 |
| ∇9 | 0.16 – 0.32 |
| ∇10 | 0.08 – 0.16 |
| ∇11 | 0.04 – 0.08 |
| ∇12 | 0.02 – 0.04 |
| ∇13 | 0.01 – 0.02 |
| ∇14 | 0.005 – 0.01 |