Hardness Conversion Calculator — HRC · HV · HB · Tensile

Hardness is measured several different ways, and the numbers do not interconvert by any exact formula — each scale presses a different indenter with a different load and measures a different thing. Rockwell C presses a diamond cone and reads a depth; Vickers presses a diamond pyramid and measures the diagonal of the impression; Brinell presses a tungsten-carbide ball and measures the width of the dent. Converting between them relies on empirical tables built from measuring the same steels on every scale — which is what ASTM E140 and ISO 18265 are. This tool interpolates those published tables, so the numbers trace back to a standard rather than to a made-up equation.

The single most important caveat is material. The conversion used here is E140 Table 1, which is for non-austenitic steels: carbon steels, alloy steels and tool steels in the usual as-forged, annealed, normalised or quenched-and-tempered conditions. It is not valid for austenitic stainless (304, 316), for aluminium or copper alloys, or for cast iron — each of those has its own conversion table because the indenter behaves differently in them. Using a steel table on a stainless part is a real and common error, and it can be off by a meaningful margin.

The second caveat is range. Brinell using the standard tungsten-carbide ball tops out around 650 HB, which is about HRC 60 — press a ball much harder than that and the ball itself starts to flatten, so the reading loses meaning. That is why this calculator returns a Brinell figure up to about HRC 58–60 and then shows a dash: not an omission, but the honest position that Brinell is out of its range there. Above it, Rockwell C and Vickers are the scales that still mean something.

The tensile-strength column is the one to treat most cautiously. There is a genuine, useful correlation for steel — roughly Rm ≈ 3.4 × HB in MPa, which is why a hardness check is often used as a quick proxy for strength on incoming material — but it assumes an unnotched, non-cold-worked steel and it drifts at high hardness, where the relationship between hardness and tensile strength stops being linear. Use it to sanity-check a certificate or to spot a mixed-up batch, not to certify a strength. Where the actual tensile property matters, it gets tested, not converted.

In the shop this tool earns its keep at goods-in and at heat-treat. A supplier certifies a shaft at 34 HRC; the drawing calls 320 HV; are those the same? A hardness file tests in HRC but the spec is Brinell — what should the meter read? A customer wants "about 40 Rockwell C, roughly what tensile is that?" All three are a read-across, and doing it against the published table rather than a half-remembered rule of thumb is the difference between a defensible inspection record and a guess.