Hardness Conversion Calculator
Different hardness scales measure the resistance of a material to permanent indentation using different indenters and loads. This calculator converts between the three most common scales used for steel: Rockwell C (HRC), Brinell (HB), and Vickers (HV), and also estimates approximate tensile strength. The conversions use polynomial regression fits to the ASTM E140 table for non-austenitic steels. These are approximations; for specification purposes, always refer to the full ASTM E140 table. Enter a known hardness value on any scale and the calculator will estimate the equivalent values on the other scales.
Hardness conversion formulas
HB from HRC: HB = 1.67 * HRC^2 / 100 + 8.57 * HRC - 30 (approx.)
HV from HB: HV = HB * 1.05 (approx. for steels)
Tensile (MPa) from HB: TS = 3.45 * HB
These are polynomial regression fits to ASTM E140 tabular data for carbon and alloy steels in the range HRC 20 to 65. Results are approximate and should not be used for material specifications.
When to use each hardness scale
Rockwell C is the fastest test for production inspection of heat-treated steel in the HRC 20 to 65 range. Brinell is preferred for castings and large forgings where surface condition or microstructural heterogeneity makes Rockwell impractical. Vickers is the most versatile method, applicable from very soft metals through ceramics, and is the basis for micro-hardness testing of thin case layers, welds, and individual phases.
Hardness conversion: frequently asked questions
What hardness scales are commonly used in materials engineering?
The most common scales are Rockwell C (HRC), Brinell (HB or HBW), and Vickers (HV). Rockwell C is standard for hard steels, Brinell is used for castings and forgings, and Vickers is a universal micro-hardness method. ASTM E140 provides conversion tables between scales.
Are hardness conversions exact?
No. Hardness conversions are approximate because each scale measures a slightly different mechanical response (penetration depth, area, or diagonal length). ASTM E140 explicitly states that conversions are not exact and should be used for comparison only, not specification.
How is tensile strength estimated from hardness?
For carbon and alloy steels, tensile strength (in MPa) is approximately 3.45 times the Brinell hardness number. This is an empirical correlation and is less reliable outside the range of about HB 100 to 400.
Why does the conversion break down at extreme hardness values?
At very low hardness (soft materials) the indenter geometry and recovery effects differ between scales. At very high hardness (above HRC 65) the Brinell method is unreliable because the ball indenter deforms. ASTM E140 defines valid conversion ranges.
Which hardness scale should I use for stainless steel?
Vickers (HV) or Rockwell B (HRB) are preferred for austenitic stainless steels because they are soft enough that HRC values would be unreliably low. For martensitic and precipitation-hardened grades after heat treatment, HRC is appropriate.
Official sources
- ASTM E140, "Standard Hardness Conversion Tables for Metals": astm.org.
- ASM International, "ASM Handbook Vol. 8: Mechanical Testing and Evaluation": asminternational.org.
- NIST, Materials Data Repository: materialsdata.nist.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.