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Brinell Hardness Number Calculator

Enter the test load, ball diameter, and measured indentation diameter.

How it is calculated

The Brinell number is the load divided by the curved surface area of the indentation: HB = 2F ÷ (π D (D − √(D² − d²))). F is the test force in kgf, D is the ball diameter in mm and d is the measured diameter of the indentation in mm. The tool requires D and d to be above zero and d not to exceed D; otherwise there is no result. It also gives a rough tensile strength, 3.45 × HB in MPa, which is a rule of thumb for steels and not valid for other metals. HB is shown to two decimals and the strength as a whole number. The tool does not check whether the load and ball size suit the material, which test standards require.

Worked example

A steel part is tested with a 10 mm ball under 3000 kgf and the indentation measures 4 mm across. Step 1: √(10² − 4²) = √84 = 9.1652. Step 2: D − 9.1652 = 0.8348, so the denominator is π × 10 × 0.8348 = 26.2275. Step 3: HB = 2 × 3000 ÷ 26.2275 = 228.77. The tool shows 228.77 and an estimated tensile strength of 3.45 × 228.77 = 789 MPa. A larger indentation under the same load would give a lower number, meaning a softer material.

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Common mistakes

  • Entering the indentation radius instead of its diameter, which gives a value far too high.
  • Using newtons instead of kgf for the force; a 29,420 N test load is 3000 kgf, and entering it unconverted makes HB about ten times too big.
  • Measuring the indentation across the wrong edge, or using the depth instead of the diameter.
  • Applying the tensile strength estimate to aluminium, copper or cast iron; the factor 3.45 is a steel rule of thumb.
  • Comparing HB values measured with different loads or ball sizes, which standard tests treat as different conditions, without noting them.

About this calculator

The Brinell hardness test presses a hardened steel or tungsten-carbide ball of known diameter into a material under a fixed load (typically 500–3000 kgf), then measures the diameter of the resulting indentation. The Brinell Hardness Number is HB = 2P ÷ (πD(D − √(D² − d²))), where P is the load, D is the ball diameter, and d is the measured indentation diameter — a larger indentation for the same load means a softer material. Along with HB, the calculator gives a rough tensile strength estimate of 3.45 × HB in MPa, a rule of thumb that suits steels only.

Because the ball leaves a relatively large, averaged impression, Brinell testing is preferred over Rockwell or Vickers for coarse-grained or non-uniform materials such as castings, forgings, and thick steel plate, where a small indenter could land on a single grain or inclusion and skew the result. Metallurgists, quality-control inspectors, and foundries use it under ASTM E10 or ISO 6506 to verify that incoming stock or finished parts meet a specified hardness range before shipping or further machining.

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