Hardness conversion chart

Technical Metal/Technical Information/Hardness conversion chart

Approximate equivalents between the Brinell and Rockwell hardness scales, as well as their rough correlation to material tensile strength.

Brinell 3000kg Load 10mm Ball Rockwell Approx Tensile Strength, psi
Diameter, mm Hardness Number B Scale C Scale
2.25 745 – 65.3 –
2.3 712 – – –
2.35 682 – 61.7 –
2.4 653 – 60 –
2.45 627 – 58.7 –
2.5 601 – 57.3 –
2.55 578 – 56 –
2.6 555 – 54.7 298,000
2.65 534 – 53.5 288,000
2.7 514 – 52.1 274,000
2.75 495 – 51 264,000
2.8 477 – 49.6 252,000
2.85 461 – 48.5 242,000
2.9 444 – 47.1 230,000
2.95 429 – 45.7 219,000
3 415 – 44.5 212,000
3.05 401 – 43.1 202,000
3.1 388 – 41.8 193,000
3.15 375 – 40.4 184,000
3.2 363 – 39.1 177,000
3.25 352 110 37.9 170,000
3.3 341 109 36.6 163,000
3.35 331 108.5 35.5 158,000
3.4 321 108 34.3 152,000
3.45 311 107.5 33.1 147,000
3.5 302 107 32.1 143,000
3.55 293 106 30.9 139,000
3.6 285 105.5 29.9 136,000
3.65 277 104.5 28.8 131,000
3.7 269 104 27.6 128,000
3.75 262 103 26.6 125,000
3.8 255 102 25.4 121,000
3.85 248 101 24.2 118,000
3.9 241 100 22.8 114,000
3.95 235 99 21.7 111,000
4 229 98.2 20.5 109,000
4.05 223 97.3 18.8 104,000
4.1 217 96.4 17.5 103,000
4.15 212 95.5 16 100,000
4.2 207 94.6 15.2 99,000
4.25 201 93.8 13.8 97,000
4.3 197 92.8 12.7 94,000
4.35 192 91.9 11.5 92,000
4.4 187 90.7 10 90,000
4.45 183 90 9 89,000
4.5 179 89 8 88,000
4.55 174 87.8 6.4 86,000
4.6 170 86.8 5.4 84,000
4.65 167 86 4.4 83,000
4.7 163 85 3.3 82,000
4.8 156 82.9 0.9 80,000
4.9 149 80.8 – –
5 143 78.7 – –
5.1 137 76.4 – –
5.2 131 74 – –
5.3 126 72 – –
5.4 121 69.8 – –
5.5 116 67.6 – –
5.6 111 65.7 – –

Hardness testing of steel is typically done on one of two scales, Rockwell or Brinell. These two scales are similar and each has equivalents on the other scale, similar to the relationship between Celsius and Fahrenheit. They differ in their testing methodology, but both are indentation hardness scales, operating on the principal that material tensile strength is directly correlated to the amount a hardened ball (or cone) will penetrate.

Rockwell

There are seven separate scales under the Rockwell umbrella, letters A-G, but the most common scales used on steel are B and C, often abbreviated HRB and HRC respectively. The B scale is typically used on softer steels, those under approximately 115,000psi tensile. Testing on the B scale involves a 1/16” steel sphere and a load of 100kgf. The testing machines then determines the amount of indention and assigns it a hardness number, example 98 HRB. Readings above 100 HRB are generally considered unreliable, so the C scale is then used. The C scale is typically used on harder steels, like those above about 110,000psi tensile. Testing on the C scale involves a 120° diamond cone and a load of 150kgf. The test is carried out the same way as the B scale test above, and the result is written as 28 HRC. Readings below 20 HRC are generally considered unreliable, so the B scale is used.

Brinell

The Brinell hardness testing method is similar to the above Rockwell testing method with a couple differences. A typical test on steel uses a 10mm diameter steel (or tungsten) ball with 3,000kg of force. A steel ball is used for most materials; the tungsten ball is used primarily for harder materials like tool steel. When a steel ball is used, the result is written as BHN or HBN, example 285 HBN. When a tungsten ball is used, the result is written as HBW, W is the chemical symbol for tungsten (wolfram). Brinell testing is generally considered to be more accurate because the larger ball size makes deeper and wider indentations, thereby averaging the test out over a wider amount of material. However, due to the larger nature of the indentations, it is often considered a destructive test.