# Steel Hardness Conversion Table: HRC, HB, HV, HRB > Cross-checked steel hardness conversion table: HRC, HB, HV, HRB, HRA and tensile strength, verified against ASTM E140-12 and ISO 18265:2013. https://www.sinbo-machining.com/wiki/reference/hardness-conversion/ --- ## On This Page - At a Glance — Which Scale When - Conversion Table — Carbon and Low-Alloy Steels - How to Convert — Step by Step - Tensile Strength from Hardness — Rough Estimate - Standards & Sources - Common Mistakes - Need hardness verification on your parts? # Steel Hardness Conversion Table Equivalent hardness values across Brinell (HB), Vickers (HV), Rockwell (HRC, HRB, HRA), and approximate tensile strength for carbon and low-alloy steels. Values cross-checked against ASTM E140-12 Table 1 and ISO 18265:2013 Annex A. Conversions are approximate — see the notes below before quoting a number on a drawing. ## At a Glance — Which Scale When | Scale | Indenter / Load | Useful range | Typical use | HB (Brinell) | 10 mm ball, 3000 kgf | ~80–650 HB | Castings, forgings, large sections, raw stock | HV (Vickers) | Diamond pyramid, 1–50 kgf | ~5–3000 HV | Thin parts, case depth, surface treatments, lab work | HRC (Rockwell C) | Diamond cone, 150 kgf | 20–70 HRC | Hardened steel, tool steel, heat-treated parts | HRB (Rockwell B) | 1/16″ ball, 100 kgf | 0–100 HRB | Soft steel, mild steel, annealed brass, aluminum | HRA (Rockwell A) | Diamond cone, 60 kgf | 20–88 HRA | Cemented carbide, thin hardened layers, very hard materials | HR15N / 30N / 45N (Superficial) | Diamond cone, 15/30/45 kgf | Various | Thin-sheet hardened surfaces, nitrided cases, coatings Lower bound of HRC Per ASTM E140 and ISO 18265, HRC conversions below ~20 HRC are unreliable — the Rockwell C diamond cone doesn’t distinguish soft materials well. Use HRB (or HB / HV) below 20 HRC. ## Conversion Table — Carbon and Low-Alloy Steels Approximate equivalent hardness values for carbon and low-alloy steels (ASTM E140-12 Table 1 & ISO 18265:2013 Annex A). To read: pick a row in your known scale, the other columns are the approximate equivalents. | HV | HB | HRC | HRA | HRB | Tensile (MPa, approx.) | 940 | — | 68.0 | 85.6 | — | — | 900 | — | 67.0 | 85.0 | — | — | 865 | 739 | 65.0 | 84.1 | — | — | 766 | 653 | 62.0 | 82.6 | — | — | 694 | 600 | 60.0 | 81.2 | — | — | 613 | 534 | 56.0 | 79.0 | — | — | 547 | 482 | 52.0 | 76.7 | — | 1740 | 505 | 461 | 50.0 | 75.5 | — | 1620 | 449 | 415 | 46.0 | 73.3 | — | 1480 | 406 | 375 | 42.0 | 71.0 | — | 1350 | 353 | 327 | 38.0 | 68.5 | — | 1180 | 316 | 293 | 34.0 | 65.8 | — | 1065 | 286 | 269 | 30.0 | 62.8 | — | 970 | 258 | 241 | 25.0 | 59.8 | 100 | 870 | 240 | 227 | 22.0 | 57.3 | 100 | 815 | 226 | 217 | 20.0 | 55.2 | 97 | 770 | 210 | 200 | (17.5) | 52.0 | 94 | 710 | 199 | 192 | (15.5) | 50.0 | 92 | 680 | 183 | 179 | (11.0) | 46.5 | 89 | 620 | 156 | 156 | — | — | 83 | 530 | 129 | 131 | — | — | 74 | 440 | 105 | 107 | — | — | 62 | 360 | 90 | 95 | — | — | 52 | 310 Parenthesized HRC values (e.g. (17.5), (15.5), (11.0)) lie outside the reliable range of the Rockwell C scale (per ISO 18265 §5) and are listed only as estimates — do not cite them on drawings. Use HRB or HV instead. ## How to Convert — Step by Step 1- Know the material family. The table above is for carbon and low-alloy steels. For austenitic stainless (304, 316), tool steels, or non-ferrous alloys, ASTM E140 has different sub-tables — using the wrong one introduces 5–15% error. 1- Pick the most authoritative measured scale. HV (Vickers) is the most linear and the one ISO 18265 recommends as the reference. If you only have HRC, that’s fine above 20 HRC; below, switch to HRB / HB / HV. 1- Use the closest row, not interpolation. Standards are discrete. Don’t average two rows — round to the nearest listed value and report the scale you actually measured. 1- Cite both scales on the drawing. If a spec says “42–48 HRC”, the supplier may measure HV. Cite the range in both systems (e.g., “42–48 HRC ≈ 419–490 HV”) to avoid rejects. ## Tensile Strength from Hardness — Rough Estimate For carbon and low-alloy steels in the as-quenched-and-tempered condition, tensile strength (MPa) can be approximated from Brinell hardness: σUTS (MPa) ≈ 3.45 × HBEmpirical relation (ISO 18265:2013, Annex A.2). Valid 150–450 HB. Outside this range the error grows; for HB > 450 the factor drops toward 3.0. This is an estimate, not a measurement. Microstructure (martensite vs bainite vs pearlite), cold work, and alloy content all shift the real value by up to ±15%. Anything that goes on a cert or a PPAP must come from an actual tensile test (ISO 6892-1 / ASTM E8). ## Standards & Sources Primary standardsASTM E140-12 Standard Hardness Conversion Tables for Metals. Tables 1–3 cover carbon/low-alloy, austenitic stainless, and nickel alloys respectively.ISO 18265:2013 Metallic materials — Conversion of hardness values. Annexes A–G organize conversions by material family; explicitly notes conversions are approximate and “no substitute for direct measurement”. Related test method standardsISO 6506-1 Brinell · ISO 6507-1 Vickers · ISO 6508-1 Rockwell · ASTM E10 Brinell · ASTM E92 Vickers · ASTM E18 Rockwell ## Common Mistakes | # | Mistake | What goes wrong | Fix | 1 | Reporting HRC below 20 | Below 20 HRC the diamond cone barely penetrates; small reading errors mean huge hardness swings | Switch to HRB, HB, or HV below 20 HRC | 2 | Using the carbon-steel table for stainless | Austenitic stainless (304, 316) work-hardens differently; carbon-steel conversions under-read by 5–15% | Use ASTM E140 Table 2 (austenitic) or measure directly | 3 | Interpolating between rows | Hardness is not linear across scales; mid-points don’t preserve the conversion relationship | Pick the nearest row and report that value | 4 | Trusting tensile-from-hardness for design | The 3.45×HB rule has ±15% real-world scatter depending on microstructure | Use it for estimate only; for cert values do a real tensile test | 5 | Mixing HB (steel ball) and HBW (tungsten carbide ball) above 450 HB | Steel balls deform above ~450 HB; ISO requires tungsten carbide (HBW) there | Always use HBW above 450 HB; cite HBW explicitly | 6 | Comparing HRC and HRA as if linearly related | HRC and HRA use the same indenter but different loads; conversion is non-linear | Use the conversion table; never divide or multiply directly Frequently Asked Questions What is the lowest HRC value I can reliably report? Around 20 HRC. Below that, the Rockwell C diamond cone doesn’t penetrate enough to give a stable reading, and ASTM E140 / ISO 18265 list those values only in parentheses as estimates. For softer steel (annealed, normalized, or low-carbon), use HRB, HB, or HV. Can I convert HB to tensile strength for any steel? Only as a rough estimate, and only for carbon and low-alloy steels in the quenched-and-tempered condition. The rule σUTS (MPa) ≈ 3.45 × HB holds within about ±15% in the 150–450 HB range. For austenitic stainless, tool steels, or cast iron, use a different relation — and for any value that goes on a certificate or PPAP, run an actual tensile test per ISO 6892-1 or ASTM E8. Why do HV and HB not match exactly at high hardness? Two reasons. First, Brinell uses a spherical indenter and Vickers a pyramid — the deformation field is different, so the conversion drifts. Second, above ~450 HB the traditional steel ball starts to deform, so ISO requires a tungsten carbide ball (HBW). HV stays accurate to much higher values, which is why ISO 18265 uses it as the reference scale. Are HRC and HRA interchangeable? No. They use the same diamond cone indenter but at different loads (150 kgf for HRC vs 60 kgf for HRA). The relationship is non-linear; you must use the conversion table. HRC is for hardened steel in the 20–70 range; HRA is preferred for very hard materials like cemented carbide and thin hardened layers. Which hardness scale should I cite on a drawing? Cite the scale your heat-treat supplier will actually measure — usually HRC for hardened parts (42–48 HRC is typical for through-hardened steel) or HB for annealed / normalized parts. Best practice: cite a range in two scales (e.g., “42–48 HRC ≈ 419–490 HV”) so a supplier using either method can self-verify. How accurate are hardness-to-hardness conversions? ASTM and ISO both caution that conversions are approximate. Uncertainty isn’t tabulated in the standards because it varies by material, microstructure, and scale pair. Expect ±1–2 HRC of scatter for steels in the mid-range (30–50 HRC), more at the extremes. Critical parts should be measured in the scale cited on the drawing. Sources & Standards Referenced 1- ASTM E140-12: Standard Hardness Conversion Tables for Metals, Table 1 (Carbon and low-alloy steels) 1- ISO 18265:2013: Metallic materials — Conversion of hardness values, Annex A 1- ISO 6506-1: Metallic materials — Brinell hardness test — Part 1: Test method 1- ISO 6507-1: Metallic materials — Vickers hardness test — Part 1: Test method 1- ISO 6508-1: Metallic materials — Rockwell hardness test — Part 1: Test method 1- ASTM E18-20: Standard Test Methods for Rockwell Hardness of Metallic Materials 1- ISO 6892-1:2019: Metallic materials — Tensile testing — Part 1: Method of test at room temperature ## Need hardness verification on your parts? We test every heat-treated batch in-house (Rockwell, Brinell, Vickers) and report the actual measured value — not a conversion — on your material cert. [Request a Quote ](https://www.sinbo-machining.com/quote/)