Rockwell Hardness Conversion
Convert Rockwell hardness numbers between HRB, HRC, Brinell HB, and Vickers HV scales. Free materials science calculator with depth-to-hardness and cross-scale conversion per ASTM E140.
About This Calculator
The Rockwell Hardness Conversion Calculator helps engineers, metallurgists, and materials scientists convert hardness values between different measurement scales. Rockwell hardness is one of the most widely used hardness testing methods in manufacturing and quality control, using the depth of penetration of an indenter to determine a material's resistance to plastic deformation.
The calculator supports two modes: Calculate from Depth computes the Rockwell hardness number (HRB or HRC) from the measured indentation depth using the formula HR = N − h × d, where N = 130 for scale B and 100 for scale C, and h = 500. Convert to Brinell / Vickers converts an existing Rockwell hardness number to equivalent Brinell (HB) and Vickers (HV) values based on material-specific relationships derived from ASTM E140 and ISO 6508 standards.
The conversion supports seven material categories: non-austenitic steels, nickel and high-nickel alloys, cartridge brass, annealed austenitic stainless steel, copper, alloyed white iron, and wrought aluminum. Each material has unique conversion coefficients because the relationship between hardness scales depends on the material's elastic and plastic deformation characteristics.
Rockwell hardness testers are common in manufacturing facilities worldwide. In India, IS 1586 governs Rockwell testing; in the US, ASTM E18 is the standard; and in the UK, BS EN ISO 6508 applies. The HRB scale (100 kgf load, 1.5875 mm steel ball) suits copper alloys and soft steels, while HRC (150 kgf load, diamond cone) is used for hardened steels, titanium, and cast iron. The Brinell test (HB) uses a 10 mm ball with 3,000 kgf load, and Vickers (HV) uses a diamond pyramid with loads from 1 to 120 kgf.
Frequently Asked Questions
How do you calculate Rockwell hardness from indentation depth?
Rockwell hardness is calculated using HR = N - h × d, where d is the indentation depth in mm. For scale B, N = 130 and h = 500, giving HRB = 130 - 500d. For scale C, N = 100 and h = 500, giving HRC = 100 - 500d. The test uses a diamond cone or steel ball indenter under a specified load.
What is the difference between Rockwell B and Rockwell C scales?
Rockwell B (HRB) uses a 1.5875 mm steel ball indenter with a 100 kgf load and is used for softer materials like copper alloys, brass, and soft steel. Rockwell C (HRC) uses a diamond cone indenter with a 150 kgf load and is used for harder materials like hardened steel, titanium, and cast iron.
Can Rockwell hardness be converted to Brinell or Vickers?
Yes, Rockwell hardness numbers can be converted to Brinell (HB) and Vickers (HV) scales using standardized relationships from ASTM E140 and ISO 6508. The conversion is material-dependent, as different materials have different relationships between hardness scales. Non-austenitic steels, nickel alloys, brass, copper, and aluminum each have unique conversion factors.
What materials can be tested with Rockwell hardness?
Rockwell hardness testing works on a wide range of metallic materials including non-austenitic steels, nickel and high-nickel alloys, cartridge brass, annealed austenitic stainless steel, copper, alloyed white iron, and wrought aluminum. The test follows ISO 6508 for metallic materials and ISO 2039-2 for plastics.
What is a typical Rockwell hardness number for steel?
Tool steel used for knives typically has HRC 55-66. Structural steel may have HRB 70-90 or HRC 20-30 depending on heat treatment. Hardened steel components often range from HRC 40-60. The exact value depends on the steel composition and heat treatment process.
Is the Rockwell hardness test destructive?
The Rockwell hardness test is considered minimally destructive or non-destructive because the indentation left on the material surface is very small (typically less than 0.5 mm wide) and does not affect the structural integrity or function of most components or test specimens.
What is the relationship between depth and Rockwell hardness number?
The relationship is inverse: a smaller indentation depth produces a higher hardness number. The formula HR = N - 500d means that for every 0.01 mm increase in depth, the hardness decreases by 5 points on the chosen scale. A depth of 0.1 mm gives HRB = 80, while 0.06 mm gives HRB = 100.