Printed from Kezuriba (kezuriba.net/en/calc/roughness/)
Surface roughness conversion and old vs new symbols
Look up Ra, Rz, N grades, µin and the old ▽ symbols side by side. Ra–Rz correspondence is not a defined conversion but a rule-of-thumb table (tool makers’ reference charts say the same). The real ratio depends on the shape of the surface.
≈Look up
Shows the standard row closest to your input (rule of thumb). µin is calculated from your input with 1 µm = 39.37 µin.
Drawn to the values calculated from this profile (vertical scale magnified). On drawings to ISO 4287:1997 / JIS 2001 or later, Rz means maximum height; on older drawings, Rz meant the ten-point height (now RzJIS).
▤Correspondence table (approximate)
| Ra µm | Rz µm(old Ry, Rmax) | RzJIS µm(old Rz) | ▽ symbol | N grade | µin | λc mm |
|---|---|---|---|---|---|---|
| 0.012 | 0.05 | 0.05 | ▽▽▽▽ | — | (0.47) | 0.08 |
| 0.025 | 0.1 | 0.1 | ▽▽▽▽ | N1 | 1 | 0.25 |
| 0.05 | 0.2 | 0.2 | ▽▽▽▽ | N2 | 2 | 0.25 |
| 0.1 | 0.4 | 0.4 | ▽▽▽▽ | N3 | 4 | 0.8 |
| 0.2 | 0.8 | 0.8 | ▽▽▽▽ | N4 | 8 | 0.8 |
| 0.4 | 1.6 | 1.6 | ▽▽▽ | N5 | 16 | 0.8 |
| 0.8 | 3.2 | 3.2 | ▽▽▽ | N6 | 32 | 0.8 |
| 1.6 | 6.3 | 6.3 | ▽▽▽ | N7 | 63 | 0.8 |
| 3.2 | 12.5 | 12.5 | ▽▽ | N8 | 125 | 2.5 |
| 6.3 | 25 | 25 | ▽▽ | N9 | 250 | 2.5 |
| 12.5 | 50 | 50 | ▽ | N10 | 500 | 8 |
| 25 | 100 | 100 | ▽ | N11 | 1000 | 8 |
| 50 | 200 | 200 | ～ | N12 | 2000 | 8 |
| 100 | 400 | 400 | ～ | — | (3937.01) | — |
- Reference charts list the same number series for Rz (maximum height) and RzJIS (ten-point height), but in reality the ten-point height is always smaller than or equal to the maximum height.
- The ▽ symbols are the old Japanese finish marks (still seen on older Japanese drawings). Japanese charts put ▽▽▽ at Ra 0.4–1.6 while some overseas sources put it at Ra 0.2–0.8, one step apart. This table follows the Japanese charts.
- For Ra 0.1 µm, Japanese charts give a 0.8 mm cut-off; the ISO 4288 range table points to 0.25 mm.
- N grades are the old ISO 1302 notation (ISO 1302 has been withdrawn and replaced by ISO 21920-1). µin in ( ) are calculated; the rest are rounded nominal values.
↺Old and new symbols (watch out for “Rz” on drawings)
On drawings to ISO 4287:1997 (JIS B 0601:2001) or later, “Rz” means maximum height, a different quantity from the older ten-point “Rz”. Check which edition of the standard the drawing follows.
| Meaning | JIS 1982 | JIS 1994 | JIS 2001 / 2013 | ISO 4287:1997 |
|---|---|---|---|---|
| Arithmetical mean deviation (mean of absolute deviations from the mean line) | Ra (centre-line average; kept as Ra75 in an annex from 1994) | Ra | Ra | Ra |
| Maximum height (highest peak + deepest valley) | Rmax | Ry | Rz | Rz |
| Ten-point height (mean of 5 highest peaks + 5 deepest valleys) | Rz | Rz | RzJIS | (deleted) |
| Root mean square deviation | — | — | Rq | Rq |
| Total height (highest to lowest point over the evaluation length) | — | — | Rt | Rt |
| Mean width of profile elements (mean spacing of peaks and valleys) | — | Sm | RSm | RSm |
⟷Cut-off and evaluation length
The sampling length equals the cut-off λc and the evaluation length is normally 5 times that. Choose by RSm (feed marks) for periodic surfaces such as turned or milled ones, and by Ra/Rz for non-periodic surfaces such as ground ones. Follow the drawing if it specifies a cut-off.
| λc mm | Evaluation length mm | Ra range µm (ISO 4288) | Rz range µm | RSm range mm |
|---|---|---|---|---|
| 0.08 | 0.4 | >0.006–0.02 | >0.025–0.1 | >0.013–0.04 |
| 0.25 | 1.25 | >0.02–0.1 | >0.1–0.5 | >0.04–0.13 |
| 0.8 | 4 | >0.1–2 | >0.5–10 | >0.13–0.4 |
| 2.5 | 12.5 | >2–10 | >10–50 | >0.4–1.3 |
| 8 | 40 | >10–80 | >50–200 | >1.3–4 |
▥Typical Ra by process
The range on which two references agree. Actual values vary widely with material, tool and conditions.
📚Sources
- Mitsubishi Materials — SURFACE ROUGHNESS (From JIS B 0601-1994) / Relationship between arithmetical mean (Ra) and conventional designation (reference data) mmhm.co.jp
- MISUMI — [Technical Data] Surface Roughness JIS B 0601(1994), Excerpts from JIS B 0031(1994) id.misumi-ec.com
- NIST — NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically nist.gov
- Haas Automation — Surface Roughness Gauges – 09-0702 haascnc.com
- STRACK NORMA — Oberflächenbeschaffenheit / Surface condition (DIN 4768-1: Conversion of Ra in Rz and vice versa) strack.de
- Noritake noritake.co.jp
- Keyence keyence.co.jp
- Taylor Hobson — Exploring Surface Texture: A fundamental guide to the measurement of surface finish (6th edition, January 2009) southampton.ac.uk
- Evident evidentscientific.com
- Mitutoyo America — Quick Guide to Surface Roughness Measurement (Bulletin No. 2229, Dec. 2016) mitutoyo.com
- MISUMI Europa — Machining processes and associated surface roughness uk.misumi-ec.com