Brinell Hardness Number Calculator

About the Brinell Hardness Number Calculator

The Brinell hardness test is one of the oldest and most widely used methods for measuring the hardness of metals and alloys. Developed by Swedish engineer Johan August Brinell in 1900, the test presses a hardened steel or tungsten carbide ball into the surface of a material under a known force, then measures the diameter of the resulting indentation.

The Brinell Hardness Number (BHN) is calculated by dividing the applied force by the curved surface area of the indentation. Higher BHN values indicate harder materials—lead scores around 5 while hardened tool steels reach 600 or more. The test is particularly well-suited for materials with coarse or uneven grain structures, such as castings and forgings, where the large indentation averages out local variations.

This calculator lets you enter the test force, ball diameter, and indentation diameter to compute the BHN, along with indentation depth, contact area, and an approximate ultimate tensile strength for steels. A built-in reference table of common materials helps identify unknown samples by comparing measured hardness values.

When This Page Helps

The Brinell hardness test is the industry standard for quality control in foundries, forges, and material receiving departments. By calculating BHN here, engineers can verify incoming material meets specifications without waiting for formal lab reports.

This calculator also estimates tensile strength from hardness, enabling quick go/no-go decisions when destructive tensile testing is impractical. The reference table helps metallurgists identify unknown samples or verify heat treatment results.

How to Use the Inputs

1. Select a common material preset or enter custom test parameters.
2. Choose the force unit (kgf, N, or lbf) and enter the applied test force.
3. Choose the dimension unit (mm or inches) and enter the ball diameter D.
4. Enter the measured indentation diameter d.
5. Review the BHN, hardness category, indentation depth, and estimated UTS.
6. Compare your result with the material reference table to identify materials.

Example Calculation

Tips & Best Practices

• Always measure indentation diameter in two perpendicular directions and average them for accuracy.
• Standard test loads for 10 mm ball: 500 kgf (soft metals), 1500 kgf (medium), 3000 kgf (steels).
• Allow at least 2.5× indentation diameter between test centers and 2.5× from edges.
• For thin specimens, use a smaller ball to keep indentation depth under 1/10 of thickness.
• Tungsten carbide balls are required above BHN 450; steel balls deform at higher hardness.
• Hold the test load for 10–15 seconds for ferrous metals and 30 seconds for non-ferrous.

History of the Brinell Test

Johan August Brinell presented his hardness test method at the Paris Exposition of 1900. It quickly became the first widely standardized hardness test and remains the primary method for testing large forgings, castings, and structural steel sections more than a century later.

How the Brinell Test Works

A hardened ball of known diameter D is pressed into the material surface under a known force F for a specified dwell time. After removing the load, the diameter d of the resulting circular impression is measured with a low-power microscope. The BHN is then computed from the curved contact area rather than the projected area, making it a time-average pressure on the actual deformed surface.

Brinell vs. Other Hardness Scales

| Test | Indenter | Best For | Range | |---|---|---|---| | Brinell | Ball (1–10 mm) | Coarse-grained metals | BHN 1–750 | | Rockwell | Diamond cone or ball | Production testing | HRC 20–70 | | Vickers | Diamond pyramid | All materials, thin layers | HV 10–3000 | | Knoop | Elongated diamond | Brittle materials, coatings | HK 10–2000 |

Tips for Accurate Brinell Testing

Surface preparation is crucial: grind the test surface smooth and clean of scale, coatings, or lubricants. An uneven surface produces an oval impression that is difficult to measure accurately. For curved surfaces, use a support anvil that matches the part geometry to prevent rocking during the test.

Frequently Asked Questions

• What ball sizes are standard for Brinell testing?

  The most common ball diameter is 10 mm, but 5 mm, 2.5 mm, and 1 mm balls are also used. Ball choice depends on specimen size—the indentation should be between 24% and 60% of ball diameter.

• Why use kgf instead of Newtons for force?

  The Brinell scale was defined using kgf, and most standards (ASTM E10, ISO 6506) still report BHN in kgf/mm² units. If you measure force in Newtons, divide by 9.80665 first.

• Can BHN be converted to Rockwell or Vickers hardness?

  Approximate conversion tables exist (ASTM E140), but they are material-specific because different tests measure slightly different properties. Conversions are most reliable for carbon and alloy steels.

• What is the relationship between BHN and tensile strength?

  For many steels, UTS (MPa) ≈ 3.45 × BHN. This approximation holds reasonably well for BHN values between 100 and 450 but should not be used for non-ferrous metals.

• Why must the indentation be smaller than the ball diameter?

  If d ≥ D, the formula produces imaginary numbers because it implies the ball sank past its equator—physically impossible under normal test conditions. Typical indentation sizes range from 25% to 60% of D.

• What materials is the Brinell test best suited for?

  Brinell testing excels on coarse-grained materials like castings, forgings, and welds because the large indentation averages out grain-to-grain variations. For thin sheets or very hard materials, Rockwell or Vickers tests are preferred.