Hardness Conversion Calculator
Select the hardness scale you know, enter the measured value, and this calculator instantly converts it to all other major hardness scales: Rockwell C (HRC), Rockwell B (HRB), Rockwell A (HRA), Vickers (HV), Brinell (HB), and approximate tensile strength in MPa. Conversions follow the ASTM E140 standard for non-austenitic steels and use linear interpolation between table values.
Formula
Worked example
A steel part measures 45 HRC. From the ASTM E140 table, HRC 45 corresponds to approximately: HRA 73.1, HV 446, HB 421. Interpolating for tensile strength at HRC 40 (1296 MPa) and HRC 45 (no direct entry, interpolated to about 1170 MPa). The 0.1 resolution of the interpolation is well within the typical test scatter of +/-2 HRC.
What is hardness and why do different scales exist?
Hardness is a material's resistance to permanent deformation when a force is applied through an indentor. It is not an intrinsic material property like density, but a response that depends on the test method, indentor shape and size, load, and dwell time. Because different industries and applications developed their own test rigs, several competing scales emerged over the past 150 years and remain in daily use today. Rockwell tests (HRC, HRB, HRA) measure the depth of penetration. They are fast, non-destructive beyond a small mark, and give a direct readout, so they dominate production-floor quality control. Vickers (HV) uses a pyramidal diamond at low loads, giving excellent resolution for thin coatings, case-hardened layers, and very hard materials. Brinell (HB) uses a steel or tungsten-carbide ball at high loads, making a larger impression that averages over a wider area - useful for coarse-grained metals like cast iron. Each method has a range where it performs best, and that is why conversions between them are needed in practice.
How hardness conversion works (and where it breaks down)
Because hardness is a test-method response rather than a fundamental property, no exact mathematical relationship exists between scales. The correlations in ASTM E140 were built by testing thousands of steel specimens on multiple rigs simultaneously and tabulating the average results. The conversion is therefore empirical, not derived from first principles. For non-austenitic carbon and alloy steels the agreement is good: typically plus or minus 2 HRC units or 10-15 HV units. For austenitic stainless steels, aluminium alloys, copper alloys, and cast iron the relationships shift substantially, and ASTM E140 provides separate tables for each. Using the steel table on aluminium will give results that are systematically off by a meaningful margin. The tensile-strength correlation, sometimes called the hardness-to-UTS conversion, is even more approximate: it is accurate for homogeneous wrought steel but unreliable for castings, welds, and surface-treated parts where the bulk hardness does not represent the actual failure mechanism.
Guide to the major hardness scales
Rockwell C (HRC): the workhorse for hard steels. Uses a 120-degree diamond cone (Brale indentor) under a 150 kgf major load. Valid roughly from 20 to 67 HRC; below 20 the resolution suffers. Specified for heat-treated tool steels, case-hardening depths, and high-strength fasteners. Rockwell B (HRB): for softer metals. Uses a 1/16-inch steel ball under 100 kgf. Valid from 0 to 100 HRB, but loses resolution above 100. Common for annealed steels, copper alloys, and aluminium. Rockwell A (HRA): uses the same diamond indentor as HRC but at 60 kgf. Covers very hard materials including cemented carbides that would crack under the 150 kgf HRC load. Vickers (HV): a square pyramid diamond pressed at loads from 1 gf to 120 kgf. The geometry is self-similar so all loads give the same number (within scatter) - unlike Brinell. Ideal for thin sections, case depths, and micro-hardness mapping. Brinell (HB/HBW): a 10 mm tungsten-carbide ball at 3000 kgf (for steel) or 500 kgf (for softer metals). The large impression averages over a wider zone, which is both a strength (for heterogeneous material) and a limitation (cannot test thin sections or near edges).
Practical tips for using hardness data in engineering
When a drawing or specification quotes hardness, check which scale is intended before converting. A requirement of "HRC 58-62" for a knife blade and "HB 200-250" for a shaft housing refer to very different regions of the conversion table and are not simply interchangeable. For quality assurance on a production line, Rockwell testing is preferred because it is quick and the result is read directly. For research or thin-section work, Vickers gives more detail. For incoming inspection of rough castings or forgings, Brinell is typical because the large impression area averages out local inhomogeneities. The tensile-strength estimate from hardness is useful for rough screening ("is this bar likely to meet a 1000 MPa UTS spec?") but should not replace a tensile test for structural calculations. Hardness measures surface resistance; a tensile test measures the full cross-section under controlled strain rate.
Hardness conversion chart (ASTM E140, non-austenitic steel)
| HRC | HRB | HRA | HV (Vickers) | HB (Brinell) | Tensile (MPa) |
|---|---|---|---|---|---|
| 68 | - | 85.6 | 940 | - | - |
| 65 | - | 83.9 | 832 | - | - |
| 62 | - | 82.3 | 746 | - | - |
| 60 | - | 81.2 | 697 | - | - |
| 58 | - | 80.1 | 653 | - | - |
| 55 | - | 78.5 | 595 | - | - |
| 52 | - | 76.8 | 544 | 500 | - |
| 50 | - | 75.9 | 513 | 475 | - |
| 48 | - | 74.7 | 484 | 451 | - |
| 45 | - | 73.1 | 446 | 421 | - |
| 42 | - | 71.5 | 412 | 390 | - |
| 40 | - | 70.4 | 392 | 371 | 1296 |
| 36 | - | 68.4 | 354 | 336 | 1165 |
| 32 | - | 66.3 | 318 | 301 | 1048 |
| 28 | - | 64.3 | 286 | 271 | 951 |
| 24 | - | 62.4 | 260 | 247 | 862 |
| 20 | - | 60.5 | 238 | 226 | 793 |
| 18 | 100 | - | 230 | 219 | 758 |
| 12 | 97 | - | 204 | 194 | 669 |
| 6 | 94 | - | 180 | 171 | 593 |
| 0 | 91 | - | 160 | 152 | 524 |
| - | 87 | - | 137 | 129 | 441 |
| - | 84 | - | 122 | 115 | 393 |
| - | 81 | - | 107 | 100 | 345 |
| - | 80 | - | 103 | 95 | 331 |
Approximate equivalents for carbon and alloy steel. Values between rows are interpolated. HRB applies below HRC 20; HRA applies above HRC 20.
Frequently asked questions
Is HRC the same as Rockwell hardness?
Rockwell hardness is a family of scales, not a single one. HRC (Rockwell C) is the most common for hard steels and is what most people mean when they say "Rockwell hardness." HRB, HRA, HRD, and several superficial scales (15-N, 30-N, 45-N) are also Rockwell methods but use different indentors and loads. Always check the letter suffix to know which scale is quoted.
What is the difference between HV and HB?
Both use an impression area to define hardness but differ in geometry and scale. Vickers (HV) uses a square pyramid diamond at low-to-moderate loads and is self-similar across loads, so it applies to a very wide range including thin coatings. Brinell (HB) uses a hard ball at high loads, making a large impression that is useful for coarse materials but unsuitable for thin sections. For steel in the range of 200-400 HV the numbers are numerically close to HB, but they diverge at higher values.
How accurate is the hardness-to-tensile-strength conversion?
For wrought, homogeneous carbon and alloy steels the conversion is reasonable - typically within 5-10% of a direct tensile test in the range of 300-600 MPa UTS. Accuracy drops at very high or very low hardness, for castings and forgings with internal defects, for surface-hardened parts where the test measures the case not the core, and for non-steel materials where the steel conversion table does not apply. Use the tensile estimate for screening and preliminary design, not for structural calculations where test data is required.
Can I convert hardness for aluminium or copper using this calculator?
Not accurately. This calculator uses the ASTM E140 Table 1 data for non-austenitic steels. Aluminium and copper alloys have different elastic properties and deformation mechanisms, so the scale relationships are different. ASTM E140 includes separate tables for these materials, and a dedicated conversion should use those data. The result you get here for non-steel materials will be a rough approximation at best.
Why is HRB not shown for values above HRC 20?
The Rockwell B scale saturates near 100 HRB. At hardness values above roughly HRC 20 the Rockwell B scale is no longer reliable or distinct enough to be useful, and ASTM E140 does not provide B-scale correlations in that range. Similarly, HRC is not reliable below about 20 HRC, where the B scale takes over. The two scales are intended for different hardness regimes.
What does HRC 58-62 mean for knives and tools?
HRC 58-62 is the typical hardness target for kitchen and folding-knife blades. At this range steel is hard enough to hold a sharp edge under normal use but not so brittle that it chips easily. Tool steels for punches and dies are often in the 60-65 HRC range. Above 65-66 HRC materials become difficult to machine and prone to brittle fracture, so extreme hardness is reserved for cemented carbides and coatings.