Legacy N1–N12 roughness grades correspond to specific Ra values from 0.025 to 50 µm.
Last updated 2026-10-16
N1–N12 is a legacy shorthand for the Ra values below. Each successive value is approximately twice the previous one. Use the published rounded values when reading a legacy N-grade callout.
| Grade | Ra (µm) | Ra (µin, rounded) |
|---|---|---|
| N1 | 0.025 | 0.984 |
| N2 | 0.05 | 1.97 |
| N3 | 0.1 | 3.94 |
| N4 | 0.2 | 7.87 |
| N5 | 0.4 | 15.7 |
| N6 | 0.8 | 31.5 |
| N7 | 1.6 | 63 |
| N8 | 3.2 | 126 |
| N9 | 6.3 | 248 |
| N10 | 12.5 | 492 |
| N11 | 25 | 984 |
| N12 | 50 | 1.97e+03 |
Source: MISUMI’s Ra comparison-specimen reference table, checked 2026-10-16. A value below 0.025 µm is finer than N1; a value above 50 µm is coarser than N12. For an intermediate input, the calculator shows the next nominal grade value at or above it, explicitly as a ceiling.
ISO 4287:1997 is a withdrawn legacy parameter definition. ISO’s catalogue identifies ISO 21920-2:2021 as its replacement. Follow the edition and measurement conditions stated on the drawing.
2026-10-16: corrected the reversed N-grade calculation and checked all twelve published N/Ra pairs. For example, 12.5–50 µm corresponds to N10–N12, and 0.4–6.3 µm to N5–N9. This check does not establish that a particular machining process will achieve a stated finish. Read the recorded check scope or report a correction.
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