Hardness conversion chart: Rockwell, Brinell, Vickers, Knoop, and tensile.

Hardness conversion tables per ASTM E140 and ISO 18265. Rockwell C (HRC), Rockwell B (HRB), Vickers (HV), Brinell (HB), Knoop (HK), and approximate ultimate tensile strength in MPa for steels. Use the right table for the right material — these conversions are empirical and material-specific.

How to use this chart

Hardness conversion is approximate, not exact. The same metal indented with different test methods produces different numerical results because each test has different indenter geometry, load, and depth of indentation. ASTM E140 standardizes empirical conversions for specific material classes — most reliably for unalloyed and low-alloy steel in the hardness range HV 200–800.

To use the tables: find your known hardness in the leftmost column, then read across to the converted scale. The tables below cover the practically useful range for engineering materials.

Tensile-from-hardness approximation

This relationship holds within ±10% for unalloyed and low-alloy steel in the hardness range HV 200–650. Outside this range (very soft annealed steel or fully martensitic case-hardened steel above HV 650), the relationship breaks down. For non-ferrous metals it is not valid at all.

Hardened steels — HRC primary scale

Use this table for through-hardened or case-hardened carbon and alloy steels in the typical hardness range HRC 20–65. Source: ASTM E140 Table 1.

Softer steels — HRB primary scale

Use this table for unhardened steel, low-carbon steel, copper, brass, and cast iron in the range HRB 60–100. The Brinell scale (3000 kg load, 10 mm carbide ball) is typically the field method of choice in this range because the larger indentation averages out surface roughness.

Non-ferrous metals — typical hardness ranges

For non-ferrous metals, ASTM E140 conversions to Rockwell or Brinell are not valid across the board. Use Vickers HV directly. Reference values for common engineering alloys:

Indian steel grades — hardness on production

Production hardness for common Indian engineering steels after standard heat treatment, useful for incoming inspection acceptance ranges:

Notes on accuracy

Hardness conversions are statistical correlations from large empirical datasets, not exact mathematical relationships. The standard says so explicitly:

• ASTM E140 itself warns: "These conversions are approximate only. The hardness value obtained for a specific material by one test method may differ significantly from that converted to another scale via these tables."
• Material composition matters. The tables above are calibrated for unalloyed and low-alloy steels. Cast irons, high-alloy steels, and case-hardened parts can deviate by ±50 HV from the table value.
• Surface condition matters. Decarburized surfaces read soft. Cold-worked surfaces read hard. Always test on a properly-prepared (machined or ground) surface, not as-received.
• Indentation size matters. Vickers at 1 kg load and Vickers at 30 kg load produce slightly different numerical results on the same material. Always cite the load with the value: HV1, HV5, HV10, HV30.

5 common hardness mistakes

1. Testing too close to an edge or another indentation. Each indentation needs at least 2.5× its own diagonal of clearance from any other indent or edge. Closer than that and you measure the deformed zone of the previous indent.
2. Wrong load for the section thickness. Vickers HV30 on a 0.5mm sheet measures the supporting anvil as much as the sheet itself. Use Vickers HV1 or Knoop HK500 for thin sections.
3. Converting case hardness to tensile. A case-hardened gear with surface HRC 60 has approximate surface tensile of 2400 MPa per the chart, but the core tensile is much lower — typically 1100 MPa for EN36. The gear will fail at core tensile, not surface tensile.
4. Testing as-received surfaces. Rolled, drawn, or forged surfaces have cold-worked layers that read 50–100 HV harder than the bulk. Always grind or machine the surface before testing.
5. Single-point testing for production acceptance. Hardness varies across a part. Most standards require 3–5 readings at specified locations and acceptance based on average or all-pass.

References

• ASTM E140-12b(2019) — Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness
• ISO 18265:2013 — Metallic materials — Conversion of hardness values
• ASTM E384-22 — Standard Test Method for Microindentation Hardness of Materials
• ASTM E10-18 — Standard Test Method for Brinell Hardness of Metallic Materials
• ASTM E18-22 — Standard Test Methods for Rockwell Hardness of Metallic Materials

For interactive conversion with custom inputs, see the Hardness Conversion Calculator. For material weight and density references, see the Material Weight Calculator.