Hardness Conversion Chart
Approximate hardness equivalents across the three scales you'll see most often on a print or mill cert, for steel.
| Rockwell C (HRC) | Brinell (HB) | Vickers (HV) |
|---|---|---|
| 20 | 226 | 238 |
| 25 | 253 | 266 |
| 30 | 286 | 302 |
| 35 | 327 | 345 |
| 40 | 371 | 392 |
| 45 | 421 | 446 |
| 50 | 481 | 513 |
| 55 | 545 | 595 |
| 60 | — | 697 |
| 65 | — | 739 |
Brinell testing isn't normally used above about HRC 58–60, which is why those rows show no value.
Why there's no clean formula here
Unlike the other calculators on this site, hardness scales don't convert by a fixed equation — each scale measures a different physical response (depth of a diamond cone indent for Rockwell, indent diameter of a hardened ball for Brinell, indent diagonal of a diamond pyramid for Vickers), and the relationship between them is empirical, published as a lookup table in ASTM E140 rather than derived from a formula. This chart shows commonly published approximate equivalents for steel at round HRC values; treat numbers between these rows as rough interpolation, not exact.
This table is for steel specifically
The HRC-to-HB-to-HV relationship shifts for other alloy families — the same Rockwell reading on a stainless steel, an aluminum alloy, or a nickel superalloy doesn't map to the same Brinell or Vickers number it would on plain carbon steel. If you're converting a hardness spec for anything other than steel, use the material-specific table in ASTM E140 rather than this chart.
What these numbers are actually telling you
Higher hardness generally means better wear resistance and edge retention, but also more difficult machining, slower cutting speeds, and faster tool wear — a print calling out HRC 55 rather than HRC 25 on an otherwise identical part is telling you to expect a much tougher job, not just a stronger one.