About

Brinell hardness testing, governed by ISO 6506, determines resistance of metallic materials to permanent indentation. The test presses a tungsten carbide ball (or hardened steel ball for softer metals) of diameter D into a specimen under a known force F, then measures the resulting indentation diameter d. Errors in reading d by even 0.05 mm can shift the computed hardness by 5 - 15 HBW on hard steels. Incorrect force-to-ball-diameter ratios violate the standard and produce non-comparable results. This calculator applies the exact ISO 6506 formula and validates that your F/D² ratio falls within a recognized test condition. It assumes the indentation is circular and the surface is flat and polished per standard preparation requirements.

The designation follows the format HBW D/F/t, where t is dwell time in seconds (typically 10 - 15 s). For steel balls (legacy), the designation is HBS. This tool computes both and flags out-of-range conditions. Pro tip: always measure indentation diameter at two perpendicular directions and average them before entering d.

Formulas

The Brinell Hardness Number represents the applied force divided by the curved surface area of the indentation. The ISO 6506 formula is:

HBW = 2FπD(D − √D² − d²)

Where F = applied test force in kgf (kilogram-force). D = diameter of the indenter ball in mm. d = mean diameter of the indentation in mm, averaged from two perpendicular measurements d₁ and d₂.

For valid results the indentation diameter must satisfy 0.24D ≤ d ≤ 0.6D. Values outside this range indicate incorrect force selection. The force-to-diameter-squared ratio F/D² must match a standard value: 1, 2.5, 5, 10, 15, or 30. If force is provided in N or kN, the conversion is 1 kgf = 9.80665 N.

Reference Data

Material Group	Ball ∅ D mm	Force F kgf	F/D² Ratio	Typical HBW Range	Dwell Time s
Steel & Cast Iron	10	3000	30	90 - 650	10 - 15
Steel & Cast Iron	5	750	30	90 - 650	10 - 15
Steel & Cast Iron	2.5	187.5	30	90 - 650	10 - 15
Steel & Cast Iron	1	30	30	90 - 650	10 - 15
Copper & Copper Alloys	10	1000	10	35 - 200	10 - 15
Copper & Copper Alloys	5	250	10	35 - 200	10 - 15
Copper & Copper Alloys	2.5	62.5	10	35 - 200	10 - 15
Light Metals (Al, Mg)	10	500	5	15 - 100	10 - 15
Light Metals (Al, Mg)	5	125	5	15 - 100	10 - 15
Light Metals (Al, Mg)	2.5	31.25	5	15 - 100	10 - 15
Lead & Tin Alloys	10	100	1	3 - 20	10 - 15
Lead & Tin Alloys	5	25	1	3 - 20	10 - 15
Titanium Alloys	10	3000	30	200 - 400	10 - 15
Nickel Alloys	10	3000	30	100 - 450	10 - 15
Zinc & Zinc Alloys	10	1000	10	30 - 130	10 - 15
Zinc & Zinc Alloys	5	250	10	30 - 130	10 - 15
Bearing Metals (Babbitts)	10	100	1	10 - 35	10 - 15
Wrought Aluminum	10	500	5	20 - 130	10 - 15
Cast Aluminum	10	2500	25	45 - 140	10 - 15
Brass	10	1000	10	50 - 180	10 - 15

Frequently Asked Questions

Per ISO 6506, the indentation diameter d must fall between 0.24D and 0.6D. If d is below 0.24D, the force is too low for reliable measurement. If d exceeds 0.6D, the indentation is too large and the ball may deform plastically, invalidating the test. In either case, select a different F/D² ratio.

HBW denotes tests using a tungsten carbide (WC) ball indenter, the current ISO 6506 standard. HBS refers to the legacy hardened steel ball. Steel balls deform above approximately 450 HBS and are no longer permitted in the standard for hard materials. All modern Brinell testing uses tungsten carbide balls. This calculator computes the number identically for both but labels the output accordingly based on your indenter selection.

The specimen thickness must be at least 8 times the indentation depth. Indentation depth h can be approximated as D − √D² − d²2. If the sample is too thin, the indentation will bulge the opposite face, producing artificially low hardness values. For a 10 mm ball test on steel, minimum thickness is typically 6 - 10 mm.

Material anisotropy, surface irregularities, and slight machine misalignment cause non-circular indentations. Measuring d₁ and d₂ at 90° and averaging them as d = (d₁ + d₂) ÷ 2 compensates for ovality. If the difference between the two exceeds 5%, the test is suspect and should be repeated.

Direct mathematical conversion between Brinell, Rockwell, and Vickers scales does not exist because the tests measure different physical properties. Empirical conversion tables (ASTM E140) provide approximate equivalents. For carbon and alloy steels, a rough approximation is: Vickers ≈ HBW for values below 350. Tensile strength in MPa ≈ 3.45 × HBW for steels. These are approximations only and should not replace proper testing.

The result is technically valid mathematically but non-standard. It cannot be compared to published hardness tables, reported per ISO 6506, or used in material certification. Standard ratios are 1, 2.5, 5, 10, 15, and 30. This calculator flags non-standard ratios with a warning and still computes the result for reference purposes.