Hardness Converter

Convert between Brinell (HB), Rockwell (HRC/HRB), Vickers (HV), and approximate tensile strength using ASTM E140.

Calculator
Presets

ASTM E140 Reference Data

HRC HV HB HRB Tensile (MPa) ~Mohs

How to Use

  1. 1
    Enter a hardness value

    Type any known hardness number into the input field — for example, 30 HRC or 200 HB.

  2. 2
    Select the source scale

    Choose the scale your value is measured in: Brinell (HB), Rockwell C (HRC), Rockwell B (HRB), or Vickers (HV). Or click a preset button.

  3. 3
    Read the converted results

    The tool instantly displays equivalent values on all four scales, an approximate Mohs rating, estimated tensile strength, and a typical material at that hardness level.

FAQ

Why are hardness conversions approximate?
Each scale uses a different indenter shape, load, and measurement method. ASTM E140 provides empirically derived correlation tables, not exact mathematical conversions. Results can vary ±5% depending on the material’s microstructure, work-hardening state, and surface finish.
What is the difference between Brinell and Rockwell hardness?
Brinell (HB) uses a 10 mm tungsten-carbide ball with 3 000 kgf and measures the diameter of the indent. Rockwell C (HRC) uses a diamond cone with 150 kgf and measures depth. Brinell suits softer metals and castings; Rockwell C is standard for hardened steels above roughly 20 HRC.
Which hardness scale should I use for my material?
Hardened steels and tool steels: Rockwell C (HRC). Softer steels, brass, and aluminum: Rockwell B (HRB) or Brinell (HB). Thin sheets, coatings, and ceramics: Vickers (HV). Non-metallic minerals: Mohs scratch test.
Can Mohs hardness be used for metals?
Mohs is a scratch-resistance scale designed for minerals. Most engineering metals fall between Mohs 4 and 7. The mapping is very rough — useful only as a quick sanity check, not for specification work.
What is the difference between macro and micro hardness tests?
Macro tests (Brinell, Rockwell) apply loads above 1 kgf and average over a larger area. Micro tests (Vickers below 1 kgf, Knoop) measure individual grains or thin coatings. Both can be mapped through ASTM E140, but micro tests require metallographic surface prep.

About

Hardness testing is one of the oldest and most widely used methods for evaluating the mechanical properties of metals. The concept dates to 1722, when Réaumur compared the scratch resistance of metals to minerals, but modern indentation hardness began with Johan August Brinell’s landmark presentation at the 1900 Paris Exposition. Brinell proposed pressing a hardened steel ball into a surface under a known load and measuring the resulting impression—a method still in daily use more than 120 years later.

In 1919, Stanley P. Rockwell patented a differential-depth machine that could test finished parts on the production floor without damaging them. His Rockwell C scale became the de facto language for specifying heat-treated steel. A year later, Robert L. Smith and George E. Sandland at Vickers Ltd. introduced a diamond-pyramid indenter that works across the entire range from soft copper to cemented carbides, giving birth to the Vickers (HV) scale. Together, these three scales cover the full spectrum of engineering metals—from dead-soft annealed copper at 50 HV to tungsten-carbide composites exceeding 1,500 HV.

ASTM International published the first edition of E140 (Standard Hardness Conversion Tables for Metals) in 1953, unifying decades of empirical correlation data. Today E140 is the global reference for converting between Brinell, Rockwell, Vickers, and approximate tensile-strength values. The conversions are inherently approximate because each test measures a slightly different mechanical response—plastic flow for Brinell, elastic recovery for Rockwell, and pyramid geometry for Vickers. Despite this, the tables agree with real-world lab data to within a few percent for most carbon and alloy steels, making them indispensable in materials selection, quality control, and failure analysis.

Modern hardness testing remains essential across industries. Automotive manufacturers specify minimum case-hardness for gears and bearings using HRC. Aerospace engineers verify titanium forging hardness with Vickers micro-indentation. Oil-and-gas pipelines require Brinell readings to confirm weld-zone toughness. Even the Mohs scratch scale, originally designed for minerals, sees use in estimating the abrasion resistance of metal surfaces in mining and earthmoving equipment.

How to Use

  1. 1
    Enter the Hardness Value and Scale

    Type in your measured hardness number and select the scale: Rockwell B or C (HRB/HRC), Vickers (HV), Brinell (HBW), or Knoop (HK).

  2. 2
    Select the Target Hardness Scale

    Choose the hardness scale you need to convert to — for example, converting an HRC reading to HV for weld procedure qualification documentation.

  3. 3
    Read the Converted Value and Equivalent Tensile Strength

    The converted hardness and the approximate ultimate tensile strength (UTS) estimate for carbon and low-alloy steels are displayed, with a note on the applicable composition range of the conversion.

About

Hardness testing is one of the most widely performed mechanical tests in materials processing and quality control because it is fast, low-cost, and essentially non-destructive. The four major scales — Rockwell, Vickers, Brinell, and Knoop — each serve different applications and material types, and converting between them is a daily requirement in manufacturing, heat treatment verification, and weld inspection.

ASME and ASTM provide standard hardness conversion tables (ASTM E140) that cover carbon steels, alloy steels, and austenitic stainless steels separately, acknowledging that the relationship between scales is material-specific. The AlloyFYI Hardness Converter implements these standard tables with interpolation for values between tabulated points, and appends the ASTM A370 tensile strength estimate for steels to provide immediate engineering context. Understanding the limitations of these conversions — particularly for non-standard materials and surface treatments — is as important as knowing the converted value itself.

FAQ

Why can't hardness conversions be exact?
Hardness scales measure different aspects of a material's resistance to indentation — Brinell uses a large ball indenter averaging over microstructural features, Vickers uses a diamond pyramid over a small area, and Rockwell measures depth under specific load-unload sequences. Because each test interrogates slightly different material volumes and deformation mechanisms, conversion between scales requires empirical correlation tables derived from testing many materials. Conversions are statistically valid only for specific material families (carbon steel, stainless steel, aluminum) and can deviate significantly for hardened tool steels, cast irons, or highly anisotropic materials.
What is the relationship between hardness and tensile strength for steels?
For carbon and low-alloy steels in the range 80–450 HBW, there is a reliable empirical relationship: UTS (MPa) ≈ 3.45 × HBW. This is codified in ASTM A370 and widely used for quick strength estimation when a tensile test specimen cannot be taken. The relationship breaks down for austenitic stainless steels (which work-harden extensively), highly alloyed tool steels, and aluminum alloys, where separate alloy-specific correlations must be used or tensile testing performed directly.
What is the maximum hardness limit for weldable steels?
Most welding codes (AWS D1.1, ISO 15614, ASME Section IX) impose a maximum hardness limit in the heat-affected zone to prevent hydrogen-induced cracking and ensure adequate toughness. The typical limit is 350 HV (approximately 36 HRC) for structural steels in non-sour service and 248 HV (22 HRC) for steels used in H₂S-containing sour service environments per NACE MR0175/ISO 15156. Exceeding these limits may require preheat adjustment, post-weld heat treatment, or use of lower-carbon-equivalent base metal.
How do I measure hardness on a thin coating or surface layer?
Conventional Vickers or Brinell tests require that the indent depth be less than one-tenth of the coating thickness to avoid substrate influence. For thin coatings (below 50 μm), nanoindentation or micro-hardness testing (low-load Vickers HV 0.1 to HV 1) is required. Knoop hardness uses an elongated indenter that produces a shallower impression at equivalent loads, making it preferable for very hard, brittle coatings and for measuring hardness gradients in carburized or nitrided case-hardened layers.
What hardness scale is most appropriate for aluminum alloys?
Brinell (HBW with a 500 kg load and 10 mm ball) and Rockwell B or Rockwell 15T (superficial) scales are commonly used for aluminum alloys. Rockwell C (HRC) is not appropriate because the loads required for the diamond indenter would penetrate through thin aluminum sections and produce unreliable readings. Vickers at low loads (HV 5–30) is suitable for research and for assessing individual microstructural constituents. Typical values range from about 20–60 HBW for softer tempers (O, T1) to 80–150 HBW for precipitation-hardened alloys (7075-T6, 2024-T3).
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