Hardness Conversion Calculator

Each hardness test measures indentation resistance differently:

• Brinell (HB): A hardened steel or tungsten carbide ball (typically 10 mm) is pressed into the surface under a known force (typically 3000 kgf for steel). Hardness is calculated from the indent diameter: $$HB = \frac{2F}{\pi D(D - \sqrt{D^2 - d^2})}$$
• Rockwell C (HRC): A diamond cone (120° apex) is pressed with a 150 kgf major load. Hardness is read from the depth of penetration: HRC = 100 − 500h, where h is in mm. Scale range: 20–70 HRC.
• Vickers (HV): A diamond pyramid (136° between faces) at loads from 1 gf to 120 kgf. Hardness is calculated from the diagonal of the square indent: $$HV = \frac{1.854 F}{d^2}$$

Because the indenter shapes and load levels differ, conversions between scales are empirical and based on extensive testing databases. ASTM E140 provides standard conversion tables for steel, non-ferrous metals, and other materials. The polynomial approximations used in this calculator are fitted to the ASTM E140 data for carbon and alloy steels.

The approximate UTS relationship $$\sigma_{UTS} \approx 3.45 \times HB \text{ (in MPa)}$$ is a widely used empirical correlation valid for carbon and low-alloy steels in the range 120-450 HB. It is less accurate for highly alloyed steels, non-ferrous metals, and hardness values outside this range.

Important limitations: conversions are most accurate for carbon and alloy steels. For stainless steels, aluminum alloys, copper alloys, and other materials, the conversion factors differ. Always specify which standard table was used when reporting converted hardness values.

The converted values are approximations based on empirical correlations for carbon and alloy steels. Accuracy is typically ±2 HRC or ±5% for HB and HV within normal ranges. The HRC scale is only valid above approximately 20 HRC (below this, use Rockwell B scale). The approximate UTS uses the standard 3.45× multiplier for Brinell hardness and should be treated as a rough estimate — always verify with actual tensile testing for critical applications.