Hardness conversion.

What does a hardness conversion show?

A material’s hardness can be measured in several ways. Product information may quote HRC, an inspection report HV and another document HB. A hardness conversion table provides an approximate comparison between these scales. The numbers are not simply different units for the same measurement: each test examines the material surface in a different way.

For example, the 24 HRC row in the stainless steel table corresponds to approximately 248 HB, 261 HV and 99 HRB. These comparisons help interpret hardness levels reported by different methods. They do not make the numbers interchangeable. A value of 99 HRB does not indicate a harder material than 24 HRC: the letters matter as much as the number.

How HRC, HRB, HB and HV differ

Rockwell hardness is determined from the depth of indentation. The HRC scale uses a diamond cone, while HRB uses a ball; the applied loads also differ. HRC is commonly seen for harder steels and HRB for lower hardness levels. There is no simple addition or subtraction that converts every value between the two scales.

Brinell testing measures the diameter of the indentation left by a ball. Values labelled HB in this tool are Brinell comparisons; test reports may use HBW for measurements made with a carbide ball. Vickers testing measures the diagonals of an indentation made by a diamond pyramid and reports the result as HV. The load and test conditions in a report provide more detail than a hardness number alone.

Why are four results not always available?

Each scale has a useful hardness range, and a comparison table may not provide every corresponding measurement. This tool displays only supported values. An empty cell is not treated as zero, and a value outside the table is not extrapolated. For example, 57 HRC can have an HV comparison while HB and HRB remain unavailable.

Intermediate values use the data in two adjacent rows. Missing measurements are never skipped to join distant rows. The approximate sign beside a result distinguishes a conversion from a direct test. Calculated HB and HV results are displayed as whole numbers, while Rockwell comparisons use at most one decimal place. More decimal places would not make the conversion more reliable.

How should estimated tensile strength be read?

UTS means ultimate tensile strength; it is not a hardness scale. The stainless steel table gives approximately 853 N/mm² for 24 HRC. N/mm² and MPa express the same quantity. The result provides an approximate indication only within the material scope supported by the comparison data.

Intermediate values are calculated linearly between the tensile-strength values in two adjacent rows. No estimate is made if either row lacks UTS data. Actual tensile strength depends on grade and material condition. A certificate or tensile-test result is a separate measured value that cannot be replaced by this approximate comparison.

What each material group covers

The tool opens with stainless steel selected. Changing the material group selects a separate comparison table and displays only the hardness scales it supports. The new group opens with its starting value; subsequent entries use that group’s data.

• Stainless steels: the existing general comparison, not a grade-specific hardness or strength guarantee.
• Carbon and low-alloy steels: unalloyed and low-alloy steels and cast steel. Stainless and high-alloy steels are outside this table.
• Nickel and high-nickel alloys: the published comparison for nickel and alloys containing more than 50% nickel, without separate validation of every commercial grade and condition.
• Aluminium: wrought products, including rolled or forged material. Not applicable to cast aluminium.
• CuZn30 brass: 70% copper and 30% zinc. Other brasses and bronzes are not treated as equivalent.
• Copper: materials in the Nos. 102–142 group. The Brinell comparison uses a 2.032 mm strip reference; it does not automatically apply to other thicknesses or loads.

Why does the material type matter?

The same hardness number can have different comparisons in another material family. For example, 24 HRC gives 261 HV in the stainless steel table and 260 HV in the carbon and low-alloy steel table. Differences are not limited to these examples; relationships between scales can change more substantially in softer metals. Each calculation therefore uses the table for the selected material family.

ASTM E140 and ISO 18265 address the scope and limitations of hardness conversions. Their use of different tables for different material groups is important. This page does not replace the complete standard tables. Where an acceptance criterion specifies a test method, the value measured by that method is the relevant result. Hardness alone does not determine tensile strength: these values describe different properties.