Hardness Conversion Calculator
Enter a hardness value and pick the scale — every scale updates instantly (ASTM E140 tabular conversion, steel).
Formula
Scale Reference
| Scale | Indenter | Load | Typical use |
|---|---|---|---|
| HRC — Rockwell C | Diamond cone | 150 kgf | Hardened steel, tools (20–68 HRC) |
| HRA — Rockwell A | Diamond cone | 60 kgf | Carbides, thin hard layers |
| HRB — Rockwell B | 1/16 in steel ball | 100 kgf | Soft steels, aluminum, copper alloys |
| HBW — Brinell | Tungsten carbide ball | 3000 kgf | Unhardened steel, cast iron (older "HB" = same ball type) |
| HV — Vickers | Diamond pyramid | 1–120 kgf | All metals, thin sections, lab reference |
| HK — Knoop | Rhombic diamond | grams–kgf | Microhardness, brittle layers, coatings |
| HS — Shore scleroscope | Drop hammer (rebound) | — | Quick field checks, large rolls |
| HLD — Leeb | Spring impact body (D probe) | — | Portable testing of installed parts |
Sample Conversion Table (steel, ASTM E140)
| HRC | HRA | HBW | HV | HK | HS | TS (MPa) |
|---|---|---|---|---|---|---|
| 20 | 60.6 | 226 | 238 | 250 | 34 | 780 |
| 25 | 63.2 | 253 | 268 | 281 | 40 | 873 |
| 30 | 65.9 | 286 | 302 | 317 | 46 | 987 |
| 35 | 68.5 | 327 | 340 | 357 | 52 | 1128 |
| 40 | 71.2 | 371 | 381 | 401 | 58 | 1280 |
| 45 | 73.9 | 421 | 425 | 446 | 64 | 1452 |
| 50 | 76.5 | 481 | 513 | 540 | 71 | 1659 |
| 55 | 79.1 | 560 | 595 | 627 | 79 | 1932 |
| 60 | 81.7 | 654 | 697 | 732 | 87 | 2256 |
| 65 | 84.4 | — | 832 | 874 | 96 | — |
FAQ
Are hardness conversions exact?
No — scales measure different things (penetration depth vs indentation size vs rebound height). ASTM E140 tables are approximations valid for steel; aluminum, cast iron and brass each have their own tables. Always verify critical specs with an actual test on the real material.
What is the difference between HB and HBW?
The letter after HB names the ball material: HBW = tungsten carbide ball, HBS (obsolete) = steel ball. Modern standards only use carbide, so "HB" and "HBW" values are the same on today's charts.
Why is HRC only valid from 20 to 68?
Below 20 HRC the diamond indenter reads too close to the scale start for accuracy — soft materials switch to HRB (ball). Above 68 the indenter sits too shallow. This calculator marks the switch automatically.