Hardness Conversion Calculator

HRC 60 (a typical hardened tool-steel value) corresponds to approximately 595 HB, 697 HV, and 732 HK per ASTM E140.

ASTM E140 conversion chart (selected values)

The full ASTM E140-12b Table 1 covers HRC 20–68. Values between table entries are interpolated linearly by the calculator. Below HRC 20 the Rockwell C scale loses reliability and E140 does not provide conversions.

The hardness scales

Rockwell C (HRC) uses a diamond cone indenter under a 150 kgf load. It is the shop-floor standard for hardened steel — fast, non-destructive, and directly readable. Range: HRC 20–68 for steel.

Brinell (HB) uses a 10 mm carbide ball under 3000 kgf. The large indentation averages out grain-structure effects, making Brinell the preferred scale for castings, forgings, and raw stock where the microstructure is coarse. It is slower than Rockwell because the indent must be measured under a microscope.

Vickers (HV) uses a diamond pyramid under variable load. Because the pyramid geometry is self-similar at any load, HV values are comparable across a wide hardness range and are the standard for research, thin coatings, and case-depth profiling (micro-hardness).

Knoop (HK) uses an elongated diamond pyramid designed for thin layers, brittle materials, and small features. The long, shallow indent reduces cracking risk in ceramics and measures case depth at very small scales.

When to use which scale

Use HRC for quick shop-floor checks on hardened parts (springs, cutting tools, gears). Use HB for incoming inspection of forgings, castings, and bar stock. Use HV for heat-treatment research, thin coatings (DLC, TiN, chrome), and weld-zone surveys. Use HK for ceramics, glass, and ultra-thin case layers where Vickers would crack the surface.