Different methods use different loads, indenter shapes, and penetration depths, so the same material will read differently depending on the scale. Conversion charts are empirical correlations, not exact equations.

Only as an estimate. Conversion tables are useful for quick comparisons and material selection, but if your specification calls for a particular hardness test (e.g., Rockwell C), you must test in that scale. Converted values should not be used for final acceptance in critical applications.

Microstructure matters. Two steels with the same chemical composition but different heat treatments (quenched, tempered, case-hardened) can yield different indentation behaviors, affecting conversion accuracy.

Approximate tensile strength correlations exist (e.g., Brinell hardness to MPa), but they are material-dependent. For carbon and low-alloy steels, the relationship is fairly reliable. For aluminum, titanium, or tool steels, it’s less consistent. Use only as a rough estimate.

Vickers (HV) is the most versatile as it works on thin materials, coatings, and across a wide hardness range. However, it requires a microscope to measure the indent. Rockwell is quicker for shop-floor hardness testing but less universal.

No, conversions are metal-specific. Non-metals require specialized tests (e.g., Shore for plastics, Knoop for ceramics).

Not all scales overlap across the full hardness range. For example, Rockwell B is not valid for hardened steels above ca 100 HRB. When the indentation becomes too shallow or too deep for a given scale, no reliable conversion exists.

Hardness numbers are unitless because they’re derived from indentation depth, load, or impression size, and then normalized in the test method’s formula. That’s why you see “HRC 60” or “200 HBW” rather than MPa or psi.