Rockwell vs Brinell vs Vickers: Metal Hardness Scales Explained (with Conversion Table)

Quick verdict

Three hardness scales dominate engineering drawings. Pick the right one and your material certifications, machinist conversations and incoming inspection all run smoothly. Pick wrong and you’ll be re-testing parts on the loading dock.

• Rockwell (HRA, HRB, HRC) — fast, cheap, the default for most steels. Used on production lines.
• Brinell (HB) — better for soft and inhomogeneous metals like castings. Larger indentation averages over voids.
• Vickers (HV) — the most precise; works on thin coatings and very hard materials. Slower and requires optical measurement.

How each test works

Rockwell hardness (HR)

A diamond cone or steel ball is pressed into the test surface under a preliminary load (10 kgf), then a major load (60-150 kgf depending on scale). The depth difference between the two loads is converted directly to a hardness number on the test machine.

Common Rockwell scales:

Rockwell is the production default because the test takes 10-30 seconds, requires no surface preparation beyond a flat spot, and the result reads directly off the dial. Most steel certifications come back in HRC.

Brinell hardness (HB / HBW)

A 10 mm tungsten carbide ball is pressed into the surface under a 3,000 kgf load (for steels) or 500 kgf (for soft metals). After 10-15 seconds, the load is removed and the diameter of the resulting indent is measured with an optical microscope. Hardness is calculated from the indent diameter using a published table.

Why Brinell still matters: the large 10 mm indenter averages out porosity and microstructure variation that smaller indenters miss. Castings, large forgings, and inhomogeneous materials are typically tested with Brinell because the smaller Rockwell indenter would land in a void or hard inclusion and read incorrectly. The Brinell number is conservative and reliable for production castings.

Brinell is slower (1-2 minutes per test, plus optical measurement), and requires more skill to read consistently. The notation HBW (W = tungsten ball) replaced the older HB notation; for engineering use they’re interchangeable.

Vickers hardness (HV)

A diamond pyramid (136° between opposite faces) is pressed into the surface under a load between 1 gf and 100 kgf depending on application. The diagonal of the resulting indent is measured optically and converted to hardness using a formula.

Why Vickers wins on precision:

• One scale covers everything from soft lead to diamond-tipped tools (HV 5 to HV 3,000+)
• Works on very thin layers (microhardness HV 0.1) — useful for coatings, case-hardened layers, weld HAZ
• Self-similar indentations (geometry stays the same regardless of load) — direct comparison across applications

Vickers is slow (1-3 minutes per test plus optical measurement) and expensive equipment, so it’s used in materials labs and incoming inspection rather than production line.

Conversion between the three scales

There’s no exact mathematical conversion — the relationship depends on material, microstructure and which scale you start from. ASTM E140 publishes the standard conversion tables for steel (the only material where conversion is reliably accurate). Here’s a practical excerpt:

Critical caveat: this table is for carbon and low-alloy steels. For aluminum, brass, copper alloys, stainless and tool steels, the conversions are different. For non-steel materials, always test on the scale specified by the alloy data sheet.

Which scale to pick for your application

If your drawing says “55 HRC” but the material is actually a tool steel that’s been treated to 60 HRC equivalent in HV — the certificate may show 60 HV but functionally the part is harder than the spec wanted. Always include the scale, the value, AND the indent location on the drawing callout.

Common engineer mistakes

1. Mixing scales without conversion

Drawing says “HV 250” but the receiving inspection only has a Rockwell tester. They report HRC 22, but HV 250 ≈ HRC 22 only for steel. If the material is actually heat-treated 6061-T6, HV 250 doesn’t translate cleanly.

Fix: Specify the scale that matches the verification capability of the receiving party. If you don’t know what they have, ask before sending the part.

2. Specifying HRC on soft material

A 6061-T6 aluminum part with “HRC 35” is impossible — HRC range starts at HRC 20 (and 6061 isn’t that hard regardless of treatment). The drawing goes back, the supplier wastes time, the schedule slips.

Fix: For aluminum, use HRB or HBW. For copper alloys, HRB or HBW. HRC is for steel.

3. Forgetting to specify the load

“HV” without a load is ambiguous — HV 1 (1 kgf, microhardness) gives different results from HV 30 (30 kgf, standard). Same for HRB at different ball sizes (1.6 mm, 3.175 mm).

Fix: Write the full callout: “HV 1” or “HV 30” or “HRC 60-62”. Don’t write just “HV 350” without context.

4. Tested wrong location on the part

A welded part tested at the weld root reads soft (HAZ effect); same part tested 20 mm away reads at base-metal hardness. The reported number is meaningless without location.

Fix: Specify on the drawing where to test (“on flat face away from welds”, “in heat-affected zone, 5 mm from weld toe”, etc.).

5. Confusing HBW and HB

Older drawings show “HB 200”; modern drawings show “HBW 200”. The difference: HBW is a tungsten carbide ball (newer standard, ASTM E10), HB was a steel ball (older). Both give equivalent numbers in the 100-300 range; HBW is mandatory above 300.

Fix: For new drawings, always use HBW. If you receive an old print with “HB” callout, treat it as HBW for production.

A practical hardness specification checklist

Before sending any drawing with a hardness callout:

• Specify scale AND value: “HRC 58-62”, not just “60”
• For HV, include the load: “HV 30 = 600-650”
• For HBW, modern symbol: “HBW 250 ± 25” (with ball/load shown if non-standard)
• Specify test location if material is non-uniform (welds, heat-treated zones, plating)
• Match the scale to the material — HRC for steel, HRB/HBW for soft metals, HV for thin layers
• Specify whether hardness is measured before or after surface treatment (anodize / paint changes nothing, but case-hardening matters)
• Match the scale to the verification capability of receiving inspection

FAQ

Is hardness the same as strength?

Closely related, not identical. For most steels, tensile strength ≈ HBW × 3.45 (in MPa). Hardness is faster to test than tensile strength, so production lines use it as a proxy. For aluminum, copper and stainless, the relationship is different and less reliable — never substitute hardness for tensile testing on critical parts.

Why isn’t there one universal hardness scale?

Each scale was developed for a different application and material range. Rockwell is fast for production. Brinell averages over voids (good for castings). Vickers is precise across all materials. They coexist because each is best at its niche. Modern materials labs typically have all three machines.

Can I test hardness on a finished CNC part?

Yes — for most steels and aluminum alloys, Rockwell or Brinell on a flat spot on the part is fine. The indent is small (under 0.5 mm for HRB, ~1 mm for HBW) and easy to remove or hide on a non-cosmetic face. For cosmetic CNC parts, designate a “hardness test pad” — a small flat area on a B-surface that won’t be visible after assembly.

What’s the hardness of common materials I’d use?

• 6061-T6 aluminum: ~95 HBW (HRB ~52)
• 7075-T6 aluminum: ~150 HBW (HRB ~87)
• Mild steel (1018, annealed): ~125 HBW
• 4140 alloy steel (annealed): ~200 HBW
• 4140 (heat-treated): 28-32 HRC
• D2 tool steel (heat-treated): 58-62 HRC
• Hardened bearing steel (52100): 60-67 HRC
• Carbide cutting insert: 88-95 HRA

For specific material specs, see our materials library — every alloy has typical hardness values listed alongside mechanical properties.

How do I check a hardness report on a material certificate?

Material certs from reputable mills include both tensile data and hardness. Cross-check that the hardness value falls within the expected range for the alloy and temper. If 6061-T6 reports as “60 HBW”, that’s wrong (typical is 95 HBW) and the cert is suspect. Ask for re-test or a different lot.