Hardness Converter
Convert between Rockwell (HRC, HRB, HRA), Vickers (HV), Knoop (HK), and Brinell (HB). Conversions are approximations per ASTM E140 and are valid mainly for non-austenitic carbon and alloy steels.
Valid HRC range: 20 – 68
HRCInput
45
Rockwell C
HRB
—
Rockwell B
HRA
72.9
Rockwell A
HV
451
Vickers
HK
459
Knoop
HB
428
Brinell
Approximate tensile strength (steels only)
≈ 1530 MPa (222 ksi)
Per ASTM A370 / SAE J417. Valid only for unalloyed and low-alloy carbon steels; does not apply to austenitic stainless, tool steels at very high hardness, or non-ferrous alloys.
Notes
- Conversions per ASTM E140-12b for non-austenitic steels. For austenitic stainless, copper alloys, aluminum, etc., use scale-specific tables — direct measurement is always preferred for critical work.
When to use which scale
- HRB — soft to medium materials (annealed steels, brass, aluminum bronze).
- HRC — hardened steels, carburized cases, tool steels; the scale is valid from 20 to 70 HRC.
- HV — universal scale; works on the same sample from soft matrix through hard precipitates.
- HK — Knoop's elongated indent fits next to edges and into thin layers (case depth, coatings).
- HB — bulk hardness on castings and forgings; loses accuracy above ~650 HBW (about 60 HRC).
Limits of conversion
- ASTM E140 conversions apply to non-austenitic carbon and alloy steels. Stainless, copper, aluminum, and titanium have different curves.
- Conversions are not exact — published agreement is typically ±1 HRC at best.
- For acceptance testing or specifications, use the scale called out in the spec; do not substitute a converted value.
- HB readings above ~650 (≈ 60 HRC) are unreliable; the carbide ball begins to deform.