Hardness Scale Converter (Vickers, Rockwell, Brinell, Shore)

What Is Hardness? Hardness is a material’s resistance to permanent surface deformation — scratching, indentation, or penetration. Unlike tensile strength or ductility, hardness is a surface property that depends on how the test is performed. Different hardness tests use different indenters, loads, and measurement methods, producing different but related scales. No single hardness test covers all materials — each scale is best suited to specific hardness ranges and materials.

Vickers Hardness (HV) The Vickers test uses a diamond pyramid indenter pressed into the surface under a known load (1–120 kgf). The diagonal of the square indentation is measured under a microscope. HV = 1.854 × F / d² (where F = load in kgf, d = diagonal in mm) Advantages: works across a very wide range (10 HV for very soft materials to 2,000+ HV for ceramics), produces a very small indentation. Range: covers soft metals to the hardest tool steels and ceramics.

Rockwell Hardness (HRB, HRC) Rockwell tests measure indentation depth under a fixed load using a diamond cone (Rockwell C) or ball indenter (Rockwell B). HRC (Rockwell C): for harder materials (case-hardened steels, HSS, carbide). Range: 20–70 HRC. HRB (Rockwell B): for softer steels, aluminum, and copper alloys. Range: 60–100 HRB. Advantages: fast, simple, no microscope needed, widely used in production environments. HRC 60 ≈ the hardness of a quality steel drill bit. HRC 64–68 = typical high-speed steel cutting tools.

Brinell Hardness (HB / HBW) The Brinell test presses a hardened steel or carbide ball under a heavy load (usually 3,000 kgf for steel) into the surface. HB = (2F) / (π × D × (D − √(D² − d²))) Advantages: gives a large indentation — better average over heterogeneous microstructures (cast iron, forgings). Disadvantage: cannot be used on thin parts or very hard materials (over ~630 HB). HB 200 = typical mild structural steel. HB 400–500 = wear-resistant steels. Above HB 600: use Vickers.

Knoop Hardness (HK) Knoop uses an elongated pyramid indenter for very small, shallow indentations. Best for thin coatings, surface-hardened layers, ceramics, and microhardness testing. One diagonal is approximately 7× longer than the other — measures only the long diagonal.

Shore Hardness (A and D) Shore tests measure rubber and plastic hardness using a spring-loaded pointed indenter. Shore A: soft rubbers (erasers, seals). Shore D: harder plastics, hard rubbers. Shore is fundamentally different from Vickers/Rockwell/Brinell — conversion to those scales is approximate.

Tensile Strength Correlation For steels, Vickers hardness correlates with ultimate tensile strength (UTS): UTS (MPa) ≈ HV × 3.3 A steel with HV 200 ≈ 660 MPa tensile strength. This relationship is empirical and varies between steel grades.

Mohs Scale Comparison The Mohs scale (1–10) is for minerals only and is not linearly related to hardness. Mohs 10 (diamond) corresponds to approximately HV 10,000. Mohs 7 (quartz) ≈ HV 1,100. Steel ≈ Mohs 5–6.