Hardness Converter
There is no universal hardness formula. Conversions are empirical, published as tables, and valid only for the material class they were measured on — so pick the class first. This calculator returns the nearest published row of ASTM E140 / ISO 18265, refuses values outside it, and leaves a cell empty where the standard prints none. A real GET form: computes correctly with JavaScript off.
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Why one hardness table is not enough
Each hardness test measures something slightly different. Rockwell C presses a diamond cone and reads a depth; Brinell presses a ball and measures the width of the dent; Vickers presses a pyramid and measures its diagonal. Relating them means measuring the same specimens on several machines and fitting a curve — and that curve depends on how the material deforms. Austenitic stainless work-hardens heavily under the indenter, so it sits on a different curve from carbon and low-alloy steel; applying the carbon-steel table to a 304 sheet is the most common hardness-conversion error there is. ASTM E140 therefore publishes separate tables per class, and the tensile-strength column of the non-austenitic table is explicitly an approximation, not a substitute for a tensile test.
Hardness conversion — frequently asked
What is 45 HRC in Brinell?
For carbon and low-alloy steel, the ASTM E140 table prints rows at 44 HRC (409 HB, 434 HV) and 46 HRC (432 HB, 458 HV) but none at 45. This calculator returns the nearest published row and says which one it used, rather than interpolating a value the standard never measured. For austenitic stainless the answer is different again — switch the material class.
Why is there no HRC value below 20?
On soft material the Rockwell C diamond barely penetrates, so the reading loses resolution and repeatability. ASTM E140 stops printing HRC below 20 for that reason, and the correct scale in that range is Rockwell B. This calculator leaves the cell empty there rather than showing a number the standard declines to publish.
Can I use a hardness test instead of a tensile test?
Not for a certificate. The tensile column here is a correlation with roughly ±15 % scatter, useful for a quick sanity check on incoming material or a heat treatment, and for nothing that has to be signed. Where a specification calls for a tensile value, it means a tensile test on a specimen — a hardness reading cannot replace it, and no standard treats it as equivalent.
Why does 304 stainless need a different table?
Because austenitic grades work-harden strongly. Under the indenter the surface hardens as it deforms, so the relationship between the scales differs from carbon steel — and it differs again between thin sheet and annealed plate, which is why ASTM E140 publishes those as two separate tables. Reading a 304 sheet against the carbon-steel table gives a number that looks reasonable and is simply wrong.