Different testing scales are used to measure the hardness of various materials. In mechanical engineering and manufacturing, Brinell (BHN), Rockwell B (HRB), and Rockwell C (HRC) are commonly used hardness scales.
Sometimes, a material’s hardness is tested on one scale, while the drawing, material specification, or engineering requirement specifies the hardness on a different scale. In such cases, an approximate equivalent hardness value can be obtained using a hardness conversion table.
For example, if a steel component has a hardness of 300 BHN, its approximate Rockwell hardness value can be determined from the table.
Important: Converted hardness values are approximate. For actual hardness measurement, it is preferred to perform direct hardness test according to the required material and applicable test method. ASTM E140 specifically describes the conversion as an approximate process.
Want to learn more about hardness? Visit our What is Hardness? articles to learn more about hardness, its types, and the different hardness testing methods used in mechanical engineering.
Brinell to Rockwell Hardness Conversion Table
Table: Conversion of Hardness Numbers — Approximate Equivalent Numbers
| Brinell Hardness Number (BHN) | Rockwell Scale B (HRB) | Rockwell Scale C (HRC) |
|---|---|---|
| 739 | — | 65 |
| 722 | — | 64 |
| 705 | — | 63 |
| 688 | — | 62 |
| 670 | — | 61 |
| 654 | — | 60 |
| 634 | — | 59 |
| 615 | — | 58 |
| 595 | — | 57 |
| 577 | — | 56 |
| 560 | — | 55 |
| 543 | — | 54 |
| 525 | — | 53 |
| 512 | — | 52 |
| 496 | — | 51 |
| 481 | — | 50 |
| 469 | — | 49 |
| 455 | — | 48 |
| 443 | — | 47 |
| 432 | — | 46 |
| 421 | — | 45 |
| 409 | — | 44 |
| 400 | — | 43 |
| 390 | — | 42 |
| 381 | — | 41 |
| 371 | — | 40 |
| 362 | — | 39 |
| 353 | — | 38 |
| 344 | — | 37 |
| 336 | 109.0 | 36 |
| 327 | 108.5 | 35 |
| 319 | 108.0 | 34 |
| 311 | 107.5 | 33 |
| 301 | 107.0 | 32 |
| 294 | 106.0 | 31 |
| 286 | 105.5 | 30 |
| 279 | 104.5 | 29 |
| 271 | 104.0 | 28 |
| 264 | 103.0 | 27 |
| 258 | 102.5 | 26 |
| 253 | 101.5 | 25 |
| 247 | 101.0 | 24 |
| 243 | 100.0 | 23 |
| 237 | 99.0 | 22 |
| 231 | 98.5 | 21 |
| 226 | 97.8 | 20 |
| 219 | 96.7 | 18 |
| 212 | 95.5 | 16 |
| 203 | 93.9 | 14 |
| 194 | 92.3 | 12 |
| 187 | 90.7 | 10 |
| 179 | 89.5 | 8 |
| 171 | 87.1 | 6 |
| 165 | 85.5 | 4 |
| 158 | 83.5 | 2 |
| 152 | 81.7 | 0 |
Note: “—” indicates that the corresponding Rockwell B value for this range is not provided in the table or is not applicable.
Important Note on Hardness Conversion:
The values in this hardness conversion chart are approximate equivalent values. Hardness scales do not have a perfectly exact one-to-one conversion because the conversion can vary with material, composition, microstructure, and heat treatment.
Therefore, the table should be used as a reference for hardness conversion. For critical engineering applications, the required hardness should be checked using the specified hardness testing method and scale.
Conclusion
The values provided in the table are intended for quick engineering reference. Since hardness relationships can vary with material and condition, the converted value should be treated as an approximate value rather than an exact measurement.