Hardness Conversion Calculator

Rockwell, Brinell, Vickers, and Knoop tests each press a differently shaped indenter into the surface under different loads and measure the resulting impression differently, so their raw numbers are not the same physical quantity. Standards like ASTM E140 exist specifically because converting between them requires an empirical correlation built from paired measurements on real samples, not a simple unit conversion.

The calculator multiplies the derived Brinell hardness number by roughly 3.45, a widely used rule-of-thumb approximation for steels that relates Brinell hardness to ultimate tensile strength in megapascals. It is meant for quick cross-checks against a specification, not as a substitute for an actual tensile test.

Both use a diamond indenter and are common for microhardness testing of small or thin samples, but Knoop leaves a shallower, more elongated impression, which makes it better suited to very thin coatings or brittle materials where a Vickers indenter might crack the surface. Their numeric scales are close but not identical, which is why this calculator treats them as separate conversion targets.

It can serve as a quick sanity check -- for example, confirming that a certificate's reported Rockwell C value falls in a plausible Brinell range using the published ASTM E140 Table 1 values -- but a table lookup is still not a direct measurement, and E140 itself notes converted values should not replace an actual test. A formal acceptance decision should rely on the material's actual certified test report or a direct re-measurement on the specified scale.