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 test covers everything, and each scale suits a particular hardness range and material family.

Vickers Hardness (HV) The Vickers test uses a diamond pyramid indenter pressed into the surface under a known load, from 1 to 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 to 70 HRC. HRB (Rockwell B): for softer steels, aluminum, and copper alloys. Range: 60 to 100 HRB. Advantages: fast, simple, no microscope needed, widely used in production environments. HRC 60 is about the hardness of a quality steel drill bit. HRC 64 to 68 covers 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))) Advantage: the large indentation averages over coarse, uneven microstructures, which is exactly what cast iron and forgings have. Disadvantage: unusable on thin parts or on anything above roughly 630 HB. HB 200 is typical mild structural steel. HB 400 to 500 covers wear-resistant steels. Above HB 600, switch to 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 runs about 7 times longer than the other, and only that long one is measured.

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 works on a fundamentally different principle from Vickers, Rockwell and Brinell, so any conversion between them is rough at best.

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 runs 1 to 10, applies to minerals only, and is nowhere near linear. Mohs 10 (diamond) sits around HV 10,000, Mohs 7 (quartz) around HV 1,100, and steel lands at Mohs 5 to 6. Note what that means: the top two Mohs steps span an order of magnitude in real hardness.