Hardness Conversion HV/HB/HRC/Rm
Convert hardness values for unalloyed and low-alloy steels: Vickers HV, Brinell HB, Rockwell HRC and the tensile strength Rm estimated from hardness. Enter one value in any scale – the calculator derives the others by linear interpolation from a stored conversion table based on ISO 18265. The conversion is an approximation and valid for steel only.
Hardness Converter (HV / HB / HRC / Rm)
Approximation, for unalloyed and low-alloy steels only (ISO 18265, Table A.1). Not a substitute for a tensile test. HRC transferable from ~240 HV, HB up to ~600 HV, Rm up to ~700 HV.
Conversion
Converting …
Formulas and fundamentals
The basis is a curated conversion table based on ISO 18265, Table A.1 (formerly DIN 50150) for unalloyed and low-alloy steels. Values between the published support points are interpolated linearly. The canonical axis is Vickers hardness HV: an input in HB, HRC or Rm is first mapped back to HV via the inverse relation, then all other scales are interpolated from HV. Because the relations increase strictly monotonically, the conversion is uniquely reversible no matter which scale you start from.
There is no physical law linking hardness and tensile strength, only an empirical correlation. For steel the tensile strength is roughly Rm ≈ c · HB with a factor c of about 3.3 to 3.5; as a rough plausibility cross-check the tool additionally reports Rm ≈ 3.2 · HB. The interpolated table value remains authoritative. Note that the hardness scales use different indenters and test forces, so any conversion carries an inherent scatter.
The validity range of the stored table spans about 80 to 940 HV. Rockwell HRC is only meaningfully transferable from around 240 HV upward (below that the diamond cone barely penetrates and readings scatter widely). The Brinell relation ends at about 600 HV, the Rm relation at about 700 HV. Outside these bounds the calculator marks the affected quantity as not defined and shows a validity note.
Worked example
A quenched-and-tempered structural steel is measured at 300 HV. Since 300 HV is a stored support point, the conversion directly yields HB = 285, HRC = 29.8 and a tensile strength Rm ≈ 965 N/mm². The plausibility cross-check gives Rm ≈ 3.2 · 285 = 912 N/mm² and confirms the order of magnitude of the table value.
A soft-annealed steel sits at 150 HV. This gives HB = 143 and Rm ≈ 480 N/mm². Rockwell HRC is reported as not defined because 150 HV is well below the meaningful HRC limit of about 240 HV – the calculator shows a note accordingly.
The conversion works in reverse just as well: entering Rm = 770 N/mm² returns 240 HV, HB = 228 and HRC = 20.3. This lets you quickly estimate the required test hardness from a specified minimum tensile strength.
Frequently asked questions
Which materials does the hardness conversion apply to?
Only unalloyed and low-alloy steels per the ISO 18265 Table A.1 approach. Austenitic and stainless steels, cast iron, cemented carbide or non-ferrous metals follow their own conversion tables or none at all – the values shown here do not apply to them.
Why is Rockwell HRC not defined at low hardness?
Below about 240 HV (around 20 HRC) the Rockwell diamond cone penetrates so deeply that the reading scatters widely and can no longer be reliably mapped to HV or HB. That is why the HRC relation in the standard starts at about 20 HRC; below that the calculator reports HRC as not defined.
How accurate is converting hardness to tensile strength?
It is an empirical correlation, not a physical law. For steel the scatter is usually within a few percent, but it can be larger for deviating microstructures. The conversion does not replace a tensile test, but it works well for estimates and plausibility checks in production and incoming-goods inspection.
Can I convert from tensile strength or HRC back to HV?
Yes. Because all relations increase strictly monotonically, the conversion is unique in every direction. You can just as well start from Rm or HRC and obtain the corresponding Vickers and Brinell hardness. The calculator maps every input to HV first and interpolates from there.
Why do conversion tables from different sources differ slightly?
Because the relation is empirical and depends on the underlying test standard, the material set and rounding. Differences of a few percent between ISO 18265, the older DIN 50150 and manufacturer tables are normal. This calculator uses common published support points and interpolates linearly between them.
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