Why are hardness conversions only approximate?

The scales measure resistance to different indenters under different loads, so there is no exact formula linking them. Conversion tables like ASTM E140 are empirical correlations for steel and carry uncertainty, especially at the extremes and for non-ferrous metals.

Which scale should I use for hard steel?

Rockwell C (HRC) and Vickers (HV) suit hardened steel above about 20 HRC. Rockwell B (HRB) and Brinell (HB) are better for softer steels and non-ferrous metals. Using a scale outside its range gives unreliable numbers.

How is tensile strength estimated from hardness?

For steel, ultimate tensile strength in MPa is roughly 3.45 times the Brinell number. This tool converts your input to Brinell first, then applies that factor. It is an estimate only and does not replace a real tensile test.

Why does Vickers track Brinell closely at low values?

Both use the same kgf/mm² basis and similar indenter geometry, so below about 300 HV the two numbers are nearly equal. They diverge at high hardness because the Brinell ball begins to deform.

Can I convert hardness of aluminium or copper?

Not with this table. The correlations here are calibrated for carbon and low-alloy steel. Non-ferrous metals need their own conversion tables, and even then conversions across scales are less reliable.

Hardness Scale Conversion Chart

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Hardness testers report on different scales, but a single material has one hardness. This tool uses the ASTM E140 correlation for steel to convert a value between Rockwell C, Rockwell B, Brinell, and Vickers, and estimates the corresponding tensile strength.

How it works

There is no exact equation linking the scales because each presses a different indenter into the surface. Instead, standards bodies have measured the same specimens on every scale and tabulated the results. This tool stores a slice of that table and interpolates linearly between the two nearest rows for whichever scale you enter.

Tensile strength for steel is then estimated from the Brinell value with the long-standing rule of thumb:

UTS (MPa) ≈ 3.45 * HB

So a part at 200 HB has an approximate tensile strength of 690 MPa.

Tips and notes

Stay inside each scale’s useful range: HRC for hard steel, HRB and HB for soft steel, HV across a wide span.
Conversions are least reliable at the very top and bottom of the table and for anything that is not steel.
The tensile estimate is a planning figure only — specify a tensile test when a real strength value is required.
Vickers and Brinell agree closely below roughly 300 because they share the same kgf/mm² basis.