CNC / machinist calculator
Hardness Conversion Calculator (HRC, HB, HV)
Convert a steel hardness between the three scales machinists actually meet: Rockwell C, Brinell and Vickers. Enter a value on any one scale and this calculator returns the other two, plus an estimated ultimate tensile strength. It also shows the standard conversion chart, so you can read across a few common points at a glance. The conversions apply to steel and are approximate, as all cross-scale hardness conversions are.
- Rockwell C
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- Brinell
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- Vickers
- —
- Tensile (est.)
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How it works
The three common hardness scales measure the same property in different ways. Rockwell C presses a diamond cone and reads a depth, Brinell presses a hard ball and measures the dent diameter, and Vickers presses a diamond pyramid and measures the impression. There is no exact formula between them, so industry uses conversion tables built from measured correlations on steel, principally ASTM E140.
This calculator interpolates over that standard table across the hardened range, roughly Rockwell C twenty to sixty-five. Below about Rockwell C twenty the material is soft enough that the Rockwell B scale is used instead, so those values fall outside this tool. Because the relationships are empirical and material-dependent, treat a converted number as close but not exact, especially across wide jumps or for non-steel alloys.
The tool also estimates ultimate tensile strength from Brinell using the long-standing steel rule that tensile strength in psi is about five hundred times the Brinell number, so tensile in ksi is about half the Brinell number. That holds for steels up to around Brinell three eighty and is shown only in that range.
Worked example
Rockwell C 40 converts to about Brinell 371 and Vickers 392, an estimated tensile strength near 185 ksi - a typical hardened tool-steel or pre-hard mold-base hardness.
Hardness conversion chart (steel)
| Rockwell C | Brinell | Vickers |
|---|---|---|
| 20 | 226 | 238 |
| 25 | 253 | 266 |
| 30 | 286 | 302 |
| 35 | 327 | 345 |
| 40 | 371 | 392 |
| 45 | 421 | 446 |
| 50 | 481 | 513 |
| 55 | 560 | 598 |
| 60 | 654 | 697 |
| 65 | 739 | 832 |
Standard steel conversions (approximate, ASTM E140). The calculator interpolates between these rows for any value in range.
Frequently asked questions
How do I convert Rockwell C to Brinell?
There is no exact formula, so conversion uses a standard correlation table for steel such as ASTM E140. For example, Rockwell C 40 is about Brinell 371 and Vickers 392. This tool interpolates that table for any value in range.
Are hardness conversions exact?
No. The scales measure hardness with different indenters, so cross-scale values are empirical correlations that vary with the material. They are accurate enough for shop use on steel but should not be treated as exact, especially for non-steel alloys.
Why can't I convert a soft material?
Below about Rockwell C 20 steel is measured on the Rockwell B scale instead, because the C-scale diamond cone barely penetrates. This calculator covers the hardened range from about HRC 20 to 65 where C, Brinell and Vickers all apply.
How is tensile strength estimated from hardness?
For steel, ultimate tensile strength in psi is roughly 500 times the Brinell hardness number, so tensile in ksi is about half the Brinell value. The estimate is shown up to about Brinell 380, above which the relationship breaks down.
Does this work for aluminum or other metals?
The conversion table here is for steel. Other alloys such as aluminum and copper have their own correlations, so a steel conversion applied to them can be well off. Use a material-specific table for non-ferrous metals.
Related calculators
Sources
- Hardness comparison and conversion (Wikipedia)
- Brinell scale and tensile-strength relationship (Wikipedia)
Every formula on this page is shown and sourced. See how we verify.
These calculators are for planning and as a starting point. Recommended speeds and feeds are published starting values that vary with your specific tool, coating, machine rigidity, workholding and coolant. Always start conservative, listen to the cut, and follow your tool maker data sheet.