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# Hardness (measurement & conversion)

This page is not a universal hardness comparison facility for its own sake.
It is provided to help you compare hardness scales with a reasonable degree of confidence.

There are a number of hardness comparison calculation methods available in many publications the accuracy of which is variable and difficult to gauge without a good deal of verification work. CalQlata has therefore developed its own formulas⁽¹⁾ that it can use internally with confidence. These formulas and their accuracy can be found in the following Tables. Our aim was to keep errors within ±0.5% throughout the range although the variable nature of the documented data has made this a little challenging (see Shore below).

The following Tables include documented values, calculated {Q} values and associated errors for each set of formulas (see Comparison Charts at the bottom of this page).

CalQlata has included all the following conversion formulas in a hardness conversion calculator

## Rockwell C (HRC)

CalQlata has compared the most commonly used hardness measurement systems with Rockwell 'C'#, which is regarded as the most ubiquitous hardness test method and its Grade C the most commonly used scale.
# except Rockwell 'B' which is compared with Brinell std.

Hugh and Stanley Rockwell together invented this hardness testing method in the USA in the mid 19th century, which involves no calculations and the hardness number is read from a dial or digital display. It is more accurate and less damaging than the Brinell method, simpler and quicker to operate than the Vickers method and more reliable than the Shore hardness test.

It has numerous measurement scales: A to G, 15, 30 & 45 and measures the depth of penetration of a diamond spherocone with tip diameter of 0.2mm and an included angle of 120° or a steel ball ranging in diameter from 1.5mm to 10mm all of which can be applied with a load ranging from 15kg to 3000kg.

The operational procedure is to apply an initial load of 10kg followed by the main test load which is held for 30 seconds. The hardness number is based upon the depth of penetration.

## Vickers Hardness Number (HV)

Rockwell C vs Vickers

This test, which was devised at Vickers Ltd. by Robert Smith and George Sandland is very accurate when compared with the Brinell and Rockwell methods and may be used on sheet material but the equipment is expensive and takes longer to operate accurately.

The Vickers test is based upon the indentation of a diamond pyramid, with an included peak angle of 136°, for a period of 30 seconds. The Vickers number (HV) is the ratio of the force (F) and the square of the depth of penetration (D). The applied force is 5, 10, 20, 30, 50 or 120kg; 50kg being the norm.

HV = F ÷ (0.5393 x d²)
where d is the diagonal length of the indentation.

 HRC HV HV {Q} Error Formulas 68 940 927 1.4% HV =(223xHRC+14500)÷(100-HRC)HRC =(100xHV-14500)÷(223+HV) 67 900 892 0.9% 66 865 859 0.7% 65 832 828 0.4% 64 800 799 0.1% 63 772 772 0.1% 62 746 745 0.1% 61 720 721 0.1% 60 697 697 0.0% 59 674 675 0.1% 58 653 653 0.0% 57 633 633 0.0% 56 613 613 0.1% 55 595 595 0.0% 54 577 577 0.0% 53 560 560 0.0% 52 544 544 0.1% 51 528 528 0.0% 50 513 513 0.0% 49 498 499 0.1% 48 484 485 0.1% 47 471 471 0.1% 46 458 458 0.1% 45 446 446 0.0% 44 434 434 0.0% 43 423 423 0.1% 42 412 411 0.1% 41 402 401 0.3% 40 392 390 0.4% 39 382 380 0.5% 38 372 371 0.4% 37 363 361 0.5% 36 354 352 0.6% 35 345 343 0.5% 34 336 335 0.4% 33 327 326 0.2% 32 318 318 0.1% 31 310 310 0.1% 30 302 303 0.2% 29 294 295 0.4% 28 286 288 0.7% 27 279 281 0.8% 26 272 274 0.8% 25 266 268 0.6% 24 260 261 0.5% 23 254 255 0.4% 22 248 249 0.3% 21 243 243 0.1% 20 238 237 0.4%

## Brinell Hardness Number - std (BHN)

Rockwell C vs brinell (std)

A standard ball is used for the Brinell hardness test on materials with a BHN value of less than 450.

This test, which was devised by the Swedish engineer Dr Johan August Brinell is less accurate than the Vickers method but benefits from not actually requiring any special equipment so long as you can accurately measure the applied load, making it ideal for improvisation. However, the thickness of the test specimen must be greater than 10 times the depth of the indentation, which is not insignificant and cannot be regarded as non-destructive testing due to the size of the indentation produced.

The depth of indentation (d) is generated by applying a force 'F' to a hard steel sphere of diameter 'D' for a period of at least 15 seconds (30 seconds for nonferrous metals).
The Brinell hardness number (BHN) is calculated as follows:

BHN = F ÷ A
where A is the surface area of the indentation: A = ½πD x [D-(D²-d²)⁰ꞌ⁵]

A certain amount of intelligence is required to use this method accurately in that insufficient and/or excessive depth of impression will result in misleading or inaccurate results. The optimum depth will be between 2.5 and 4.75mm for a standard 10mm ball.

The following table is based upon a 10mm diameter ball and a force of 3000kg

 HRC BHN BHN {Q} Error Formulas 52 508 497 2.2% BHN = 122+HRC1.5HRC = 1.5√(BHN-122) 51 494 486 1.6% 50 481 476 1.1% 49 469 465 0.9% 48 455 455 0.1% 47 443 444 0.3% 46 432 434 0.5% 45 421 424 0.7% 44 409 414 1.2% 43 400 404 1.0% 42 390 394 1.1% 41 381 385 0.9% 40 371 375 1.1% 39 362 366 1.0% 38 353 356 0.9% 37 344 347 0.9% 36 336 338 0.6% 35 327 329 0.6% 34 319 320 0.4% 33 311 312 0.2% 32 301 303 0.7% 31 294 295 0.2% 30 286 286 0.1% 29 279 278 0.3% 28 271 270 0.3% 27 264 262 0.6% 26 258 258 0.1% BHN = 156+HRC1.42HRC = 1.42√(BHN-156) 25 253 253 0.1% 24 247 248 0.2% 23 243 242 0.4% 22 237 237 0.2% 21 231 231 0.1% 20 226 226 0.0%

## Brinell Hardness Number - Hultgren (BHN-H)

Rockwell C vs Brinell (Hultgren)

A spherical ball manufactured from Axel Gustaf Emanuel Hultgren's tungsten steel, which has since become known as Hultgren steel, will flatten less than a standard hardened steel ball and is used for the Brinell hardness test on materials with a BHN value of up to 500.

The same operating conditions and calculation methods are used for this test as for the Brinell standard test (see above).

The following table is based upon a 10mm diameter ball and a force of 3000kg

 HRC BHN-H BHN-H {Q} Error Formulas 60 613 613 0.0% BHN = 70+HRC1.538HRC = 1.538√(BHN-70) 59 599 599 0.0% 58 587 585 0.3% 57 575 572 0.6% 56 561 558 0.5% 55 546 545 0.2% 54 534 532 0.4% 53 519 519 0.1% 52 508 506 0.4% 51 494 493 0.2% 50 481 480 0.2% 49 469 468 0.3% 48 455 455 0.1% 47 443 443 0.0% 46 432 431 0.3% 45 421 419 0.5% 44 409 409 0.0% BHN = 129+HRC1.489HRC = 1.489√(BHN-129) 43 400 400 0.1% 42 390 390 0.1% 41 381 381 0.0% 40 371 372 0.2% 39 362 363 0.3% 38 353 354 0.3% 37 344 345 0.4% 36 336 337 0.2% 35 327 328 0.3% 34 319 320 0.2% 33 311 311 0.1% 32 301 303 0.7% 31 294 295 0.4% 30 286 287 0.4% 29 279 279 0.2% 28 271 272 0.3% 27 264 264 0.1% 26 258 257 0.4% 25 253 253 0.1% BHN = 153.4+HRC1.43HRC = 1.43√(BHN-153.4) 24 247 248 0.2% 23 243 242 0.4% 22 237 237 0.2% 21 231 231 0.1% 20 226 226 0.0%

## Brinell Hardness Number - tungsten (BHN-W)

Rockwell C vs Brinell (tungsten)

A spherical ball manufactured from tungsten carbide will flatten less than standard or Hultgren balls and is used for hard materials with a BHN value of up to 630.

The same operating conditions and calculation methods are used for this test as for the Brinell standard test (see above).

Whilst tungsten carbide balls may need to be smaller than steel balls (10mm) the accuracy of this test remains maximised by using the largest ball available. Therefore, even for very hard materials it is advisable to use a 10mm tungsten carbide ball where possible along with a suitably high load.

The following table is based upon a 10mm diameter ball and a force of 3000kg

 HRC BHN-W BHN-W {Q} Error Formulas 65 739 743 0.5% BHN = HRC1.593-30HRC = 1.593√(BHN+30) 64 722 724 0.2% 63 705 705 0.0% 62 688 687 0.2% 61 670 668 0.3% 60 654 650 0.6% 59 634 632 0.3% 58 615 614 0.1% 57 595 597 0.3% 56 577 579 0.4% 55 560 562 0.4% 54 543 545 0.4% 53 525 528 0.6% 52 512 511 0.1% 51 496 495 0.2% 50 481 479 0.5% 49 469 468 0.2% BHN = 110+HRC1.511HRC = 1.511√(BHN-110) 48 455 457 0.4% 47 443 446 0.7% 46 432 435 0.8% 45 421 425 0.9% 44 409 414 1.3% 43 400 404 1.0% 42 390 394 0.9% 41 381 383 0.6% 40 371 373 0.7% 39 362 364 0.4% 38 353 354 0.2% 37 344 344 0.1% 36 336 335 0.4% 35 327 325 0.5% 34 319 316 0.8% BHN = 143+HRC1.462HRC = 1.462√(BHN-143) 33 311 309 0.6% 32 301 302 0.2% 31 294 294 0.2% 30 286 287 0.5% 29 279 280 0.5% 28 271 274 0.9% 27 264 267 1.1% 26 258 260 0.8% 25 253 254 0.2% 24 247 247 0.1% 23 243 241 0.9% 22 237 235 0.9% 21 231 229 1.0% 20 226 223 1.4%

## Rockwell Hardness Number - A (HRA)

Rockwell C vs Rockwell A

The Rockwell A grade is suitable for extremely hard materials such as tungsten carbides, hardened high carbon steels and ceramics. It is also used for hard thin metal sheets.

The following table is based upon a diamond indenter and a force of 60kg

 HRC HRA HRA {Q} Error Formulas 68 85.6 85 0.4% HRA = 49.742+0.5229xHRCHRC = (HRA-49.742)÷0.5229 67 85 85 0.3% 66 84.5 84 0.3% 65 83.9 84 0.2% 64 83.4 83 0.2% 63 82.8 83 0.1% 62 82.3 82 0.2% 61 81.8 82 0.2% 60 81.2 81 0.1% 59 80.7 81 0.1% 58 80.1 80 0.0% 57 79.6 80 0.1% 56 79 79 0.0% 55 78.5 79 0.0% 54 78 78 0.0% 53 77.4 77 0.1% 52 76.8 77 0.2% 51 76.3 76 0.1% 50 75.9 76 0.0% 49 75.2 75 0.2% 48 74.7 75 0.2% 47 74.1 74 0.3% 46 73.6 74 0.3% 45 73.1 73 0.2% 44 72.5 73 0.3% 43 72 72 0.3% 42 71.5 72 0.3% 41 70.9 71 0.4% 40 70.4 71 0.4% 39 69.9 70 0.3% 38 69.4 70 0.3% 37 68.9 69 0.3% 36 68.4 69 0.2% 35 67.9 68 0.2% 34 67.4 68 0.2% 33 66.8 67 0.3% 32 66.3 66 0.3% 31 65.8 66 0.2% 30 65.3 65 0.2% 29 64.7 65 0.3% 28 64.3 64 0.1% 27 63.8 64 0.1% 26 63.3 63 0.1% 25 62.8 63 0.0% 24 62.4 62 0.2% 23 62 62 0.4% 22 61.5 61 0.4% 21 61 61 0.5% 20 60.5 60 0.5%

## Rockwell Hardness Number - B (HRB)

Rockwell B vs Brinell (std)

The same operational method as for the 'A' scale (see above) but this test applies to softer materials, such as low carbon steels, or steels in annealed condition and soft metals that fall below or around the lower end of the Rockwell 'C' Scale (i.e. less than 300).

A comparison is carried out using the standard Brinell test ball of 10mm and a 3000kg applied load (see BHN above) in order to facilitate a conversion with other hardness measurement systems.

 HRB BHN BHN {Q} Error Formulas 100 240 240.6 0.3% BHN = 96+1.051HRBHRB = Log₁.₀₅₁(BHN-96) 99 234 233.6 0.2% 98 228 226.9 0.5% 97 222 220.6 0.6% 96 216 214.5 0.7% 95 210 208.8 0.6% 94 205 203.3 0.8% 93 200 198.1 0.9% 92 195 193.2 0.9% 91 190 188.4 0.8% 90 185 184.0 0.6% 89 180 179.7 0.2% 88 176 175.6 0.2% 87 172 171.8 0.1% 86 169 168.1 0.5% 85 165 164.6 0.3% 84 162 161.3 0.5% 83 159 158.1 0.6% 82 156 155.1 0.6% 81 153 152.2 0.5% 80 150 149.5 0.3% 79 147 146.9 0.1% 78 144 144.4 0.3% 77 141 142.1 0.8% 76 139 139.8 0.6% 75 137 137.7 0.5% 74 135 135.7 0.5%

## Rockwell Hardness Number - D (HRD)

Rockwell C vs Rockwell D

The Rockwell D grade is for case hardened materials that need a lighter load than the C-Grade test but is otherwise identical.

The following table is based upon a diamond indenter and a force of 100kg

 HRC HRD HRD {Q} Error Formulas 68 76.9 77 0.0% HRD = 24.767+0.7667xHRCHRC = (HRD-24.767)÷0.7667 67 76.1 76 0.0% 66 75.4 75 0.0% 65 74.5 75 0.1% 64 73.8 74 0.0% 63 73 73 0.1% 62 72.2 72 0.1% 61 71.5 72 0.0% 60 70.7 71 0.1% 59 69.9 70 0.1% 58 69.2 69 0.1% 57 68.5 68 0.0% 56 67.7 68 0.0% 55 66.9 67 0.1% 54 66.1 66 0.1% 53 65.4 65 0.0% 52 64.6 65 0.1% 51 63.8 64 0.1% 50 63.1 63 0.0% 49 62.1 62 0.4% 48 61.4 62 0.3% 47 60.8 61 0.0% 46 60 60 0.1% 45 59.2 59 0.1% 44 58.5 59 0.0% 43 57.7 58 0.1% 42 56.9 57 0.1% 41 56.2 56 0.0% 40 55.4 55 0.1% 39 54.6 55 0.1% 38 53.8 54 0.2% 37 53.1 53 0.1% 36 52.3 52 0.1% 35 51.5 52 0.2% 34 50.8 51 0.1% 33 50 50 0.1% 32 49.2 49 0.2% 31 48.4 49 0.3% 30 47.7 48 0.1% 29 47 47 0.0% 28 46.1 46 0.3% 27 45.2 45 0.6% 26 44.6 45 0.2% 25 43.8 44 0.3% 24 43.1 43 0.2% 23 42.1 42 0.7% 22 41.6 42 0.1% 21 40.9 41 0.1% 20 40.1 40 0.0%

## Rockwell Hardness Number - 15-15N (HR15)

Rockwell C vs Rockwell 15-15

The same operational method as for the A, B, C & D ranges applies to this hardness range but uses the '15' scale and a 15kg load.

This scale is used for materials that will result in very small indentations such as very hard materials, the harder the material the greater the load (i.e. 30kg or 45kg see below).

Two sub-scales are provided: N & T
N is for very hard materials that will result in a small indentation
T is for softer materials to minimise the indentation

The hardness values are comparable with both the above sub-scales in that any given material would show the same hardness value irrespective of the sub-scale used. Each scale, however, is better suited, and therefore more accurate and reliable if used with the appropriate materials.

The following table is based upon a diamond indenter, a force of 15kg and the 'N' sub-scale

 HRC HR15 HR15 {Q} Error Formulas 68 93.2 93 0.1% HR15 = 61.5+HRC0.82HRC = 0.82√(HR15-61.5) 67 92.9 93 0.0% 66 92.5 93 0.1% 65 92.2 92 0.0% 64 91.8 92 0.0% 63 91.4 91 0.0% 62 91.1 91 0.1% 61 90.7 91 0.1% 60 90.2 90 0.0% 59 89.8 90 0.2% HR15 = 56+HRC0.865HRC = 0.865√(HR15-56) 58 89.3 90 0.3% 57 88.9 89 0.1% 56 88.3 89 0.3% 55 87.9 88 0.1% 54 87.4 88 0.1% 53 86.9 87 0.1% 52 86.4 87 0.1% 51 85.9 86 0.1% 50 85.5 85 0.0% 49 85 85 0.0% 48 84.5 84 0.0% 47 83.9 84 0.1% 46 83.5 83 0.1% 45 83 83 0.1% 44 82.5 82 0.1% 43 82 82 0.1% 42 81.5 81 0.2% 41 80.9 81 0.1% 40 80.4 80 0.1% 39 79.9 80 0.1% 38 79.4 79 0.2% 37 78.8 79 0.1% 36 78.3 78 0.1% 35 77.7 78 0.1% 34 77.2 77 0.1% 33 76.6 77 0.0% 32 76.1 76 0.1% 31 75.6 75 0.1% 30 75 75 0.1% 29 74.5 74 0.1% 28 73.9 74 0.1% 27 73.3 73 0.0% 26 72.8 73 0.1% 25 72.2 72 0.0% 24 71.6 72 0.0% 23 71 71 0.1% 22 70.5 70 0.0% 21 69.9 70 0.0% 20 69.4 69 0.1%

## Rockwell Hardness Number - 30-30N (HR30)

Rockwell C vs Rockwell 30-30

The same operational method as for the '15' scale (see above) but uses the '30' scale and a 30kg load.

This scale is used for materials that will result in very small indentations such as very hard materials, the harder the material the greater the load (i.e. 15kg see above or 45kg see below).

Two sub-scales are provided: N & T
N is for very hard materials that will result in a small indentation
T is for softer materials to minimise the indentation

The hardness values are comparable with both the above sub-scales in that any given material would show the same hardness value irrespective of the sub-scale used. Each scale, however, is better suited, and therefore more accurate and reliable if used with the appropriate materials.

The following table is based upon a diamond indenter, a force of 30kg and the 'N' sub-scale

 HRC HR30 HR30 {Q} Error Formulas 68 84.4 85 0.2% HR30 = 22.6+HRC0.978HRC = 0.978√(HR30-22.6) 67 83.6 84 0.1% 66 82.8 83 0.0% 65 81.9 82 0.0% 64 81.1 81 0.1% 63 80.1 80 0.0% 62 79.3 79 0.1% 61 78.4 78 0.1% 60 77.5 77 0.1% 59 76.6 77 0.1% 58 75.7 76 0.1% 57 74.8 75 0.1% 56 73.9 74 0.1% 55 73 73 0.1% 54 72 72 0.1% 53 71.2 71 0.0% 52 70.2 70 0.1% 51 69.4 69 0.0% 50 68.5 68 0.0% 49 67.6 68 0.0% 48 66.7 67 0.0% 47 65.8 66 0.0% 46 64.8 65 0.1% 45 64 64 0.0% 44 63.1 63 0.0% 43 62.2 62 0.0% 42 61.3 61 0.0% 41 60.4 60 0.0% 40 59.5 59 0.0% 39 58.6 59 0.0% 38 57.7 58 0.0% 37 56.8 57 0.0% 36 55.9 56 0.1% 35 55 55 0.1% 34 54.2 54 0.3% 33 53.3 53 0.3% 32 52.1 52 0.3% 31 51.3 51 0.1% 30 50.4 50 0.1% 29 49.5 50 0.1% 28 48.6 49 0.0% 27 47.7 48 0.0% 26 46.8 47 0.0% 25 45.9 46 0.0% 24 45 45 0.0% 23 44 44 0.2% 22 43.2 43 0.1% 21 42.3 42 0.1% 20 41.5 41 0.4%

## Rockwell Hardness Number - 45-45N (HR45)

Rockwell C vs Rockwell 45-45

The same operational method as for the '15' scale (see above) but uses the '45' scale and a 45kg load.

This scale is used for materials that will result in very small indentations such as very hard materials, the harder the material the greater the load (i.e. 30kg or 45kg see above).

Two sub-scales are provided: N & T
N is for very hard materials that will result in a small indentation
T is for softer materials to minimise the indentation

The hardness values are comparable with both the above sub-scales in that any given material would show the same hardness value irrespective of the sub-scale used. Each scale, however, is better suited, and therefore more accurate and reliable if used with the appropriate materials.

The following table is based upon a diamond indenter, a force of 45kg and the 'N' sub-scale

 HRC HR45 HR45 {Q} Error Formulas 68 75.4 75 0.1% HR45 = 0.86+HRC1.022HRC = 1.022√(HR45-0.86) 67 74.2 74 0.2% 66 73.3 73 0.1% 65 72 72 0.2% 64 71 71 0.0% 63 69.9 70 0.0% 62 68.8 69 0.1% 61 67.7 68 0.1% 60 66.6 67 0.1% 59 65.5 65 0.2% 58 64.3 64 0.0% 57 63.2 63 0.1% 56 62 62 0.1% 55 60.9 61 0.0% 54 59.8 60 0.3% HR45 = HRC1.038-2.85HRC = 1.038√(HR45+2.85) 53 58.6 59 0.3% 52 57.4 58 0.3% 51 56.1 56 0.5% 50 55 55 0.3% 49 53.8 54 0.3% 48 52.5 53 0.5% 47 51.4 52 0.3% 46 50.3 50 0.1% 45 49 49 0.3% 44 47.8 48 0.3% 43 46.7 47 0.1% 42 45.5 46 0.1% 41 44.3 44 0.1% 40 43.1 43 0.2% 39 41.9 42 0.2% 38 40.8 41 0.0% 37 39.6 40 0.0% 36 38.4 38 0.0% 35 37.2 37 0.0% 34 36.1 36 0.2% 33 34.9 35 0.2% 32 33.7 34 0.1% 31 32.5 32 0.1% 30 31.3 31 0.0% 29 30.1 30 0.0% 28 28.9 29 0.1% 27 27.8 28 0.2% 26 26.7 27 0.5% 25 25.5 25 0.4% 24 24.3 24 0.3% 23 23.1 23 0.2% 22 22 22 0.5% 21 20.7 21 0.1% 20 19.6 20 0.2%

## Shore Hardness Number (SHN)

Rockwell C vs Shore

The Shore Scleroscope (or durometer) was developed by Albert F. Shore (USA) and uses a small diamond tipped hammer weighing 1/12th of an ounce (2.36246g) in a graduated glass tube to measure the hardness of a material. The hammer is dropped from a predefined height and the measured rebound height defines the hardness of the impacted material.

This is a simple system that requires no calculation and no complicated equipment. Whilst it is not considered as accurate as the other hardness testing methods, this is only because its operation is prone to misuse. However, if correctly used and read, this method should be at least as accurate as any other.

This equipment has the added advantage of being practical to transport and use in any environment, but works best on hard materials, i.e. the results for materials such as lead will be unreliable as the rebound height will be virtually non-existent.

The greater than expected errors in the calculated results are due to the erratic nature of the documented values (see image) which, if measured accurately should follow a much smoother curve. The curve generated by the formulas (SHN {Q}) is considered (by CalQlata) to be more representative of the actual Shore values than the documented values (SHN).

 HRC SHN SHN {Q} Error Formulas 68 97 97 0.5% SHN =201.5-1.5x(125²-(36+HRC)²)⁰ꞌ⁵HRC =(125²-((201.5-SHN)/1.5)²)⁰ꞌ⁵-36 67 95 95 0.3% 66 92 93 1.2% 65 91 91 0.0% 64 88 89 1.1% 63 87 87 0.0% 62 85 85 0.1% 61 83 83 0.3% 60 81 81 0.5% 59 80 80 0.5% 58 78 78 0.1% 57 76 76 0.3% 56 75 75 0.6% 55 74 73 1.4% 54 72 71 0.9% 53 71 70 1.6% 52 69 68 1.0% 51 68 67 1.7% 50 67 65 2.3% 49 66 64 3.0% 48 64 63 2.1% 47 63 61 2.7% 46 62 60 3.3% 45 60 59 2.2% 44 58 57 1.0% 43 57 56 1.4% 42 56 55 1.8% 41 55 54 2.2% 40 54 53 2.5% 39 52 52 1.0% 38 51 50 1.2% 37 50 49 1.4% 36 49 48 1.6% 35 48 47 1.7% 34 47 46 1.8% 33 46 45 1.8% 32 44 44 0.4% 31 43 43 0.5% 30 42 42 0.6% 29 41 41 0.8% 28 41 40 1.4% 27 40 40 1.1% 26 38 39 1.8% 25 38 38 0.4% 24 37 37 0.0% 23 36 36 0.6% 22 35 35 1.2% 21 35 35 1.1% 20 34 34 0.4%

## Comparison Charts

HRC: The common comparison hardness range of values (Rockwell C). Values below 20 are ignored as their reliability varies too much between test methods.

e.g. SHN: The comparable hardness range from a documented source⁽²⁾; Brinell, Vickers, Shore, etc.

e.g. SHN {Q}: The comparable range of values calculated using the formulas in the right-hand column. The graph immediately above each Table is a plot of the documented values compared with the calculated values.

Error: The percentage difference between documented and calculated values using the formulas in the right-hand column.

Formulas: The formulas used to calculate the Q values⁽³⁾.

### Notes

1. Except for the 'Vickers' formula which can be found in numerous sources; e.g. http://link.springer.com/article/10.1007%2FBF02833189#page-2
2. Reference publication 2 (see Further Reading below)
3. These formulas have been devised by CalQlata