November 3, 2026 · Indumor
In this chapter
What is 300 HB in Rockwell? About 32 HRC, and that "about" is half of this chapter. No formula turns one hardness scale into another, because each one measures something different: Rockwell, how deep a diamond cone sinks; Brinell, the diameter of the dent a ball leaves; Vickers, the diagonal of a pyramid's mark. The relationship between them came from testing thousands of steel specimens with every method and writing down what each one gave. That table of correspondences is ASTM E140 (ISO 18265 in Europe), and it is the one printed here, from 68 down to 20 HRC, with the soft range in Rockwell B after it.
It holds for carbon and alloy steels, hardened or not, tool steels included. It does not hold for austenitic stainless, cast iron, aluminum, copper or brass, which have tables of their own. And it is approximate: the standard says so in its title. Two labs can read the same part one or two HRC points apart without either of them being wrong.
Rockwell is the fastest and the most common in the shop because the machine reads for you: a 10 kgf preload to seat the indenter, the full load (150 kgf on the C scale, 100 on B, 60 on A) and a reading of how far the indenter stayed sunk once it is released. Every 0.002 mm is one point: a 60 HRC part carries a 0.08 mm impression and a 20 HRC part a 0.16 mm one. That is where the minimum thickness rule comes from (ten times the depth of the impression with the diamond, fifteen with a ball) and the back-face rule: if it shows a bulge, the number is void.
Brinell leaves a big dent, 2 to 6 mm across with the 10 mm ball, which is an advantage on castings, forgings and rolled stock, where a small impression can land on a soft grain or an inclusion. The diameter is read with a graduated loupe and put through the formula or the table. HBW 10/3000 means a tungsten carbide ball (W), 10 mm, 3000 kgf, the setup for steel; aluminum is tested at 10/500 and copper at 10/1000, and the numbers do not mix. Vickers uses a 136° diamond pyramid and works on everything from lead to cemented carbide; it is the lab method and the one for carburized, nitrided and chrome-plated cases. For very thin cases there is also superficial Rockwell (15N, 30N): the same diamond with 15 or 30 kgf.
| Scale | Indenter | Load | What is read and how it is worked out |
|---|---|---|---|
| Rockwell C (HRC) | 120° diamond cone, 0.2 mm tip radius | 150 kgf (1471 N) 10 kgf preload | Depth h HRC = 100 − h/0,002 |
| Rockwell A (HRA) | Diamond cone | 60 kgf (588 N) | Depth h HRA = 100 − h/0,002 |
| Rockwell B (HRB) | Carbide ball 1/16 in (1.588 mm) | 100 kgf (981 N) 10 kgf preload | Depth h HRB = 130 − h/0,002 |
| Brinell (HBW 10/3000) | Carbide ball D = 10 mm | 3000 kgf (29.42 kN) 10 to 15 s | Impression diameter d (graduated loupe) formula below |
| Brinell (other loads) | 10, 5 or 2.5 mm ball | 10/500 aluminum 10/1000 copper and bronze | Diameter d same formula |
| Vickers (HV) | Diamond pyramid 136° between faces | 1 to 100 kgf (HV1 to HV100) | Mean diagonal d (microscope) HV = 0,1891 · F/d² |
| Shore (HS) | Diamond-tipped hammer dropped 254 mm (scleroscope) | – | Rebound height 0 to 140 scale |
| Leeb (HLD) | Impact body with 3 mm carbide ball (D probe) | spring, 11 N·mm | Rebound speed over impact speed HL = 1000 · vr/vi |
| Scale | Useful range | Minimum thickness | Used for |
|---|---|---|---|
| Rockwell C (HRC) | 20 to 70 HRC | ≥ 10 × h (0.8 mm at 60 HRC; 1.6 mm at 20 HRC) | Hardened steels, tools, Q&T parts |
| Rockwell A (HRA) | 60 to 93 HRA | ≥ 10 × h (0.4 mm at 80 HRA) | Cemented carbide, thin hardened sheet, nitrided cases |
| Rockwell B (HRB) | 20 to 100 HRB | ≥ 15 × h (1 to 2 mm) | Annealed and normalized steel, sheet, brass, bronze |
| Brinell (HBW 10/3000) | 95 to 650 HBW | ≥ 8 × depth (2 to 7 mm by hardness) | Large parts, castings, forgings, rolled stock |
| Brinell (other loads) | by material | ≥ 8 × depth | Non-ferrous: the numbers do not mix with 10/3000 values |
| Vickers (HV) | 5 to 3000 HV (everything) | ≥ 1.5 × d (tenths of a mm) | Cases, small parts, carbide, lab work |
| Shore (HS) | 20 to 100 HS | supported mass or ≥ 5 mm | Mill rolls; today mostly replaced by Leeb |
| Leeb (HLD) | 200 to 900 HLD | ≥ 25 mm and ≥ 5 kg (coupled with paste: ≥ 3 mm) | Portable tester: shafts, mounted parts, incoming checks |
Minimum thickness: the ASTM E18 rule (10 times the indentation depth with the diamond, 15 with a ball) and ISO 6506-1 (8 times the depth for Brinell).
The rebound scales are a separate family. The Shore scleroscope drops a small diamond-tipped hammer and measures how high it bounces; it is rarely seen now. It was replaced by Leeb (ISO 16859, ASTM A956), the handheld tester that fires a 3 mm carbide ball at the part and compares rebound speed with impact speed. It checks mounted shafts and incoming stock in seconds, with two conditions people forget: a part over 5 kg and over 25 mm thick (coupled with paste to something heavy, 3 mm will do). Do not confuse it with Shore A and D for rubber, which is a different instrument.
The Brinell values in parentheses, from 60 HRC up, are beyond the normal range of the method: the ball flattens against steel that hard. The standard lists them because they show up on old drawings, but a part that hard is measured in HRC or HV. There is no tensile strength from 60 HRC up either: the specimens break brittle before giving a number anyone would trust.
| HRC | HV | HBW 10/3000 | HRA | Shore HS | Leeb HLD approx. | UTS approx. MPa | UTS approx. ksi |
|---|---|---|---|---|---|---|---|
| 68 | 940 | – | 85.6 | 97.3 | – | – | – |
| 67 | 900 | – | 85.0 | 95.0 | – | – | – |
| 66 | 865 | – | 84.5 | 92.7 | – | – | – |
| 65 | 832 | (739) | 83.9 | 90.6 | – | – | – |
| 64 | 800 | (722) | 83.4 | 88.5 | – | – | – |
| 63 | 772 | (705) | 82.8 | 86.5 | – | – | – |
| 62 | 746 | (688) | 82.3 | 84.5 | 828 | – | – |
| 61 | 720 | (670) | 81.8 | 82.6 | 819 | – | – |
| 60 | 697 | (654) | 81.2 | 80.8 | 809 | – | – |
| 59 | 674 | 634 | 80.7 | 79.0 | 800 | 2420 | 351 |
| 58 | 653 | 615 | 80.1 | 77.3 | 791 | 2330 | 338 |
| 57 | 633 | 595 | 79.6 | 75.6 | 782 | 2240 | 325 |
| 56 | 613 | 577 | 79.0 | 74.0 | 773 | 2160 | 313 |
| 55 | 595 | 560 | 78.5 | 72.4 | 764 | 2075 | 301 |
| 54 | 577 | 543 | 78.0 | 70.9 | 755 | 2015 | 292 |
| 53 | 560 | 525 | 77.4 | 69.4 | 746 | 1950 | 283 |
| 52 | 544 | 512 | 76.8 | 67.9 | 737 | 1880 | 273 |
| 51 | 528 | 496 | 76.3 | 66.5 | 729 | 1820 | 264 |
| 50 | 513 | 481 | 75.9 | 65.1 | 720 | 1760 | 255 |
| 49 | 498 | 469 | 75.2 | 63.7 | 712 | 1695 | 246 |
| 48 | 484 | 455 | 74.7 | 62.4 | 703 | 1640 | 238 |
| 47 | 471 | 443 | 74.1 | 61.1 | 695 | 1580 | 229 |
| 46 | 458 | 432 | 73.6 | 59.8 | 687 | 1525 | 221 |
| 45 | 446 | 421 | 73.1 | 58.5 | 679 | 1480 | 215 |
| 44 | 434 | 409 | 72.5 | 57.3 | 671 | 1435 | 208 |
| 43 | 423 | 400 | 72.0 | 56.1 | 663 | 1385 | 201 |
| 42 | 412 | 390 | 71.5 | 54.9 | 655 | 1340 | 194 |
| 41 | 402 | 381 | 70.9 | 53.7 | 647 | 1295 | 188 |
| 40 | 392 | 371 | 70.4 | 52.6 | 640 | 1255 | 182 |
| 39 | 382 | 362 | 69.9 | 51.5 | 632 | 1220 | 177 |
| 38 | 372 | 353 | 69.4 | 50.4 | 625 | 1180 | 171 |
| 37 | 363 | 344 | 68.9 | 49.3 | 618 | 1145 | 166 |
| 36 | 354 | 336 | 68.4 | 48.2 | 611 | 1110 | 161 |
| 35 | 345 | 327 | 67.9 | 47.1 | 603 | 1075 | 156 |
| 34 | 336 | 319 | 67.4 | 46.1 | 596 | 1050 | 152 |
| 33 | 327 | 311 | 66.8 | 45.1 | 590 | 1025 | 149 |
| 32 | 318 | 301 | 66.3 | 44.1 | 583 | 1005 | 146 |
| 31 | 310 | 294 | 65.8 | 43.1 | 576 | 970 | 141 |
| 30 | 302 | 286 | 65.3 | 42.2 | 570 | 950 | 138 |
| 29 | 294 | 279 | 64.8 | 41.3 | 563 | 930 | 135 |
| 28 | 286 | 271 | 64.3 | 40.4 | 557 | 905 | 131 |
| 27 | 279 | 264 | 63.8 | 39.5 | 551 | 885 | 128 |
| 26 | 272 | 258 | 63.3 | 38.7 | 545 | 860 | 125 |
| 25 | 266 | 253 | 62.8 | 37.8 | 539 | 850 | 123 |
| 24 | 260 | 247 | 62.4 | 37.0 | 533 | 820 | 119 |
| 23 | 254 | 243 | 62.0 | 36.3 | 527 | 805 | 117 |
| 22 | 248 | 237 | 61.5 | 35.5 | 521 | 795 | 115 |
| 21 | 243 | 231 | 61.0 | 34.8 | 516 | 770 | 112 |
| 20 | 238 | 226 | 60.5 | 34.2 | 510 | 760 | 110 |
HB in parentheses: beyond the normal range of the ball. Leeb: indicative column (D probe), up to 62 HRC; the real conversion depends on the tester and the material. No UTS from 60 HRC up.
Between two rows, interpolate straight: 290 HB sits between 286 (30 HRC) and 294 (31 HRC), so it is 30.5 HRC. Notice that Brinell and Vickers agree up to about 240 and then drift apart (at 60 HRC, 654 against 697): that is the ball, which no longer penetrates like the pyramid, not an error in the table. Chapter 20 says what hardness each treatment reaches and chapter 19 what each steel is called under each standard.
From 240 HB down the indenter changes: a 1/16 in ball and 100 kgf, the B scale. It is the scale of annealed and normalized steels, rolled plate, brass and bronze. A normalized 1045 reads 90 to 95 HRB; mild steel, 60 to 70. Between 97 and 100 HRB (roughly 20 to 25 HRC) both Rockwell scales behave badly, one at the ceiling and the other at the floor of its range; there it is better to test Brinell or Vickers and convert.
| HRB | HV | HBW 10/3000 | UTS approx. MPa | UTS approx. ksi | HRB | HV | HBW 10/3000 | UTS approx. MPa | UTS approx. ksi |
|---|---|---|---|---|---|---|---|---|---|
| 100 | 240 | 240 | 800 | 116 | 77 | 141 | 141 | 470 | 68 |
| 99 | 234 | 234 | 785 | 114 | 76 | 139 | 139 | 460 | 67 |
| 98 | 228 | 228 | 750 | 109 | 75 | 137 | 137 | 455 | 66 |
| 97 | 222 | 222 | 715 | 104 | 74 | 135 | 135 | 450 | 65 |
| 96 | 216 | 216 | 705 | 102 | 73 | 132 | 132 | 440 | 64 |
| 95 | 210 | 210 | 690 | 100 | 72 | 130 | 130 | 435 | 63 |
| 94 | 205 | 205 | 675 | 98 | 71 | 127 | 127 | 425 | 62 |
| 93 | 200 | 200 | 650 | 94 | 70 | 125 | 125 | 420 | 61 |
| 92 | 195 | 195 | 635 | 92 | 69 | 123 | 123 | 415 | 60 |
| 91 | 190 | 190 | 620 | 90 | 68 | 121 | 121 | 405 | 59 |
| 90 | 185 | 185 | 615 | 89 | 67 | 119 | 119 | 400 | 58 |
| 89 | 180 | 180 | 605 | 88 | 66 | 117 | 117 | 395 | 57 |
| 88 | 176 | 176 | 595 | 86 | 65 | 116 | 116 | 385 | 56 |
| 87 | 172 | 172 | 580 | 84 | 64 | 114 | 114 | – | – |
| 86 | 169 | 169 | 570 | 83 | 63 | 112 | 112 | – | – |
| 85 | 165 | 165 | 565 | 82 | 62 | 110 | 110 | – | – |
| 84 | 162 | 162 | 560 | 81 | 61 | 108 | 108 | – | – |
| 83 | 159 | 159 | 550 | 80 | 60 | 107 | 107 | – | – |
| 82 | 156 | 156 | 530 | 77 | 59 | 106 | 106 | – | – |
| 81 | 153 | 153 | 505 | 73 | 58 | 104 | 104 | – | – |
| 80 | 150 | 150 | 495 | 72 | 57 | 103 | 103 | – | – |
| 79 | 147 | 147 | 485 | 70 | 56 | 101 | 101 | – | – |
| 78 | 144 | 144 | 475 | 69 | 55 | 100 | 100 | – | – |
In this range the standard gives the same number for Vickers and Brinell, down to 55 HRB; below 65 HRB no tensile value is given.
The numbers in this table are typical, not from a standard: hardness depends on the treatment, the section and the heat. They are there to orient you and to make you suspicious: if the supplier says the wear plate is 400 HB and the handheld tester reads 280, something is off. They also serve the file test, the most used hardness check in any shop: a new file sits at 62 to 66 HRC and skates on anything over 60, barely bites at 55 and cuts freely below 45. Two or three files worn to different degrees make a set of references that is rarely off by more than five points.
| Material or part | Typical hardness | On another scale | Note |
|---|---|---|---|
| SAE 1010 hot-rolled steel | 95 to 105 HB | 55 to 60 HRB | below the HRC range |
| Structural steel A36 / S235 | 120 to 160 HB | 67 to 84 HRB | plate and sections |
| SAE 1045 normalized | 170 to 210 HB | 87 to 95 HRB | Rm 580 to 720 MPa |
| SAE 1045 quenched and tempered | 20 to 30 HRC | 226 to 286 HB | depends on the temper |
| SAE 4140 quenched and tempered | 28 to 35 HRC | 271 to 327 HB | usual as-supplied condition: 28 to 32 HRC |
| "400 HB" wear plate | 370 to 430 HB | 40 to 45 HRC | chute and hopper liners |
| Spring steel (SAE 5160 / 9260, tempered) | 42 to 50 HRC | 390 to 480 HB | leaf and valve springs |
| Knife blade | 55 to 61 HRC | 595 to 720 HV | kitchen 55 to 58; field knife 58 to 61 |
| O1 tool steel, hardened and tempered | 58 to 62 HRC | 650 to 750 HV | tempered at 200 °C |
| Bearing ring (100Cr6 / SAE 52100) | 60 to 65 HRC | 700 to 830 HV | rings and balls |
| File | 62 to 66 HRC | 750 to 870 HV | why it skates on anything over 60 |
| HSS (M2), hardened | 63 to 65 HRC | 770 to 830 HV | drills, end mills, tool bits |
| Cemented carbide (WC-Co) | 1300 to 1800 HV | 89 to 93 HRA | never in HRC: the cone chips |
| Window glass | 500 to 600 HV | ≈ 50 to 55 HRC if it were steel | scratches 1045; a file scratches it |
| Gray iron EN-GJL-250 | 180 to 250 HB | – | do not convert to Rm with 3.45 |
| Annealed 304 stainless | 150 to 200 HB | 80 to 92 HRB | work-hardens fast when machined |
| Phosphor bronze CuSn8 | 90 to 140 HB | – | hard-rolled, up to 220 |
| CuZn37 brass, annealed / half-hard | 55 to 75 / 100 to 130 HB | – | own table, not the steel one |
| Annealed copper | 40 to 50 HB | – | hard-drawn: 90 to 110 |
| Aluminum 6061-T6 | 95 HB (10/500) | about 60 HRB | off the steel table (10/3000) |
| Aluminum 1050, annealed | 20 to 25 HB | – | the caliper jaw marks it |
| Lead | 4 to 5 HB | – | 10 mm ball, 100 kgf |
The Brinell and Vickers formulas turn what is measured into the number. On Rockwell the machine does the arithmetic, but it helps to know that HRC = 100 − h/0.002 and HRB = 130 − h/0.002, with h in millimeters: a "negative" Rockwell reading means a soft part, not a broken machine.
F: load in N (3000 kgf = 29420 N); D: ball diameter in mm; d: impression diameter in mm. The 0.102 converts N to kgf; with the load in kgf, drop it.
F: load in N; d: mean diagonal of the impression in mm (average of the two). With F in kgf the constant is 1.8544.
The link to tensile strength is the conversion people make most and the one that needs the most care. For carbon and low-alloy steels, the strength in MPa is roughly 3.45 times the Brinell number. It descends from the old American rule of 500 psi per Brinell point and works between 100 and 450 HB with an error of about 5 % either way, the same scatter you get between two specimens cut from the same bar; above 450 HB the factor climbs to 3.6 or 3.7. It fails for austenitic stainless, which work-hardens under the ball; for gray iron, where the relationship is something else entirely (a GJL-250 has 250 MPa at 200 HB); and for aluminum, copper and bronze.
Carbon and low-alloy steels, 100 to 450 HB (HBW 10/3000); typical error ±5 %.
Worked example · a 1045 shaft and a Q&T pinion
A normalized 1045 shaft is Brinell tested with a 10 mm ball and 3000 kgf (29420 N). The impression measures 4.20 mm. Through the formula: √(10² − 4.2²) = 9.075; 10 − 9.075 = 0.925; π × 10 × 0.925 = 29.05; 0.102 × 2 × 29420 = 6002; and 6002 / 29.05 = 207 HBW 10/3000. In the B-range table, 207 HB is about 94 HRB. By the rule, 3.45 × 207 = 714 MPa; the standard's table gives 680. That 5 % is the normal error of the conversion, not a slip in the arithmetic.
The same customer sends a 4140 pinion out to be quenched and tempered "to 30 HRC" and the certificate reads 290 HB, taken with a ball because the part is large. Between 286 (30 HRC) and 294 (31 HRC), 290 HB is 30.5 HRC: within what was asked. In Vickers, about 306 HV; the strength, 3.45 × 290 = 1000 MPa by the rule against 960 from the table.
Linear interpolation in the two tables of this chapter (ASTM E140, non-austenitic steels). Off the table it does not guess: it says so.
Aluminum, copper, brass and bronze are not converted with this table. ASTM E140 has separate tables for each family, with their own Brinell loads (500 kgf for aluminum, 1000 for copper). A 6061-T6 reads 95 HB at 10/500 and about 60 HRB; in the steel table, built on 10/3000, 100 HB is already 55 HRB and 95 HB is not even listed. Austenitic stainless has its own table too. When a drawing calls out a hardness on a non-ferrous part, test on the scale the drawing names and do not convert. The weight of those same metals is in chapter 22.
About 654 HB (carbide ball) and 697 HV per ASTM E140. At that hardness the Brinell ball is at its limit: the standard puts the value in parentheses, and the right call is to test in HRC or HV.
For carbon and low-alloy steels, UTS in MPa ≈ 3.45 × HB (or 500 psi per point): 200 HB is about 690 MPa. Valid between 100 and 450 HB; not for austenitic stainless, cast iron, aluminum or copper.
No. ASTM E140 has separate tables for aluminum, copper and brass, with different Brinell loads (500 and 1000 kgf). The steel table is built on 3000 kgf: its numbers do not mix with those.
Sources: ASTM E140-12b(2019)e1, Standard Hardness Conversion Tables for Metals; ISO 18265:2013, Conversion of hardness values; ASTM A370 (conversion tables with approximate tensile strength); ISO 6508-1 and ASTM E18 (Rockwell); ISO 6506-1 and ASTM E10 (Brinell); ISO 6507-1 (Vickers); ISO 16859-1 and ASTM A956 (Leeb).
We machine them to print, send them for heat treatment and deliver them tested in HRC, certificate included.
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