Hardness Converter — HRC, HRB, HB, Vickers, Shore & More

Each hardness test measures a different physical property: Rockwell measures indentation depth (a macro-scale depth measurement), Brinell measures indentation diameter (macro-scale width), Vickers measures indentation diagonal (micro-to-macro scale), and Shore measures rebound height (dynamic elastic response). A material that is very elastic might read differently on a depth-based scale vs. a width-based scale. Additionally, conversion relationships change with material type — steel, aluminum, and brass have different conversion curves. The only truly reliable conversion is direct testing with the specified method.

Knife hardness is typically specified in HRC (Rockwell C). Most quality kitchen knives range from HRC 55-62. Japanese chef knives: HRC 60-64 (very hard, holds edge longer but more brittle and harder to sharpen). German-style knives: HRC 55-58 (softer, easier to sharpen but needs more frequent sharpening). Budget knives: HRC 50-54. Hardness above HRC 64 becomes increasingly brittle and prone to chipping for most knife applications. Pocket knives typically run HRC 56-60. The ideal knife hardness depends on intended use — a hunting knife that might hit bone should be softer (HRC 55-58) while a fillet knife can be harder (HRC 58-62).

Rockwell B (HRB) uses a 1/16" hardened steel ball indenter with a 100 kg load, designed for softer materials (annealed steel, brass, copper, aluminum). Typical HRB range: 40-100. Rockwell C (HRC) uses a diamond cone (Brale) indenter with a 150 kg load, designed for harder materials (hardened steel, tool steel, carburized surfaces). Typical HRC range: 20-70. The "C" scale is the most widely specified hardness test in the heat treating industry. HRB below 40 should use the HRE or HRF scales with lighter loads. HRC above 70 approaches the limit of the diamond indenter and may damage it.

Brinell hardness (HBW) is widely used in structural steel specifications because the large indentation (typically 2-6 mm diameter) provides a bulk material measurement averaging out local variations. Common structural steel grades: A36 steel ≈ HB 120-140, ASTM A572 Grade 50 ≈ HB 150-180, high-strength quenched and tempered steel (A514) ≈ HB 235-300. Steel tensile strength is approximately correlated to Brinell hardness: tensile strength (psi) ≈ 500 × HB. This relationship allows non-destructive hardness testing to estimate the strength of in-service steel structures. A498 steel at HB 200 has an estimated tensile strength of 100,000 psi (690 MPa).

Shore (Durometer) hardness measures the resistance of materials to indentation by a spring-loaded indenter. It is most commonly used for elastomers (rubber), plastics, and soft metals. The A scale (Shore A) is for flexible rubbers and soft plastics (e.g., O-rings: Shore A 70, car tires: Shore A 60-75). The D scale (Shore D) is for harder plastics and semi-rigid materials (e.g., hard hat: Shore D 75, nylon gears: Shore D 80-90). Unlike Rockwell/Brinell/Vickers which use dead-weight loads, Shore uses a spring-loaded indenter and reads instantly. Shore hardness is NOT convertible to Rockwell or Brinell for soft materials due to the fundamental difference in measurement principle — this converter provides approximate equivalents only for harder materials (Shore D 50+).