MATERIAL PROPERTIES
Hardness Conversion Calculator
Hardness conversion translates a material’s measured hardness between Rockwell, Brinell, Vickers, and other scales using empirical correlation tables per ASTM E140 and ISO 18265. Enter a value in any scale to get equivalents across all supported scales, with material-family-aware accuracy for carbon steel, stainless steel, aluminum, brass, copper, and titanium.
✓ASTM E140 & ISO 18265
✓8 Hardness Scales
✓Material-Family Aware
Hardness Conversion Calculator
Select your material family, enter a value in any scale, and get all equivalents instantly.
HRC40.0
HBW371
HV390
Standard & Accuracy
ASTM E140-2019 · Carbon Steel · ±5% typical
HOW TO USE
How to Use This Hardness Conversion Calculator
Select your material family first — this is the step most generic converters skip. Enter a value in any scale and get all equivalents instantly. The tool handles HRA, HRB, HRC, HRD, HRF, HBW, HV, and tensile strength.
HRC
40.0
HBW
371
HV
390
Standard & Material
ASTM E140-2019 · Carbon Steel
HOW HARDNESS CONVERSION WORKS
What Is Hardness Conversion?
Hardness conversion translates a material’s measured hardness from one test scale to another. There is no closed-form mathematical formula; the relationships are empirical, derived from thousands of paired measurements, and published as lookup tables in ASTM E140 and ISO 18265.
Rockwell C → Brinell (Carbon Steel)
HBW ≈ 84.9 + 6.78 × HRC + 0.014 × HRC²
Empirical fit per ASTM E140
Valid 20–68 HRC
Tensile Strength from Brinell (Steel)
UTS (MPa) ≈ 3.45 × HBW
Per ASTM A370
Does not apply to stainless or aluminum
Worked Example: HRC to HBW to HV
A drawing specifies 40 HRC. The QC lab needs Brinell and Vickers equivalents for a carbon steel part. Using the ASTM E140 table:
40
HRC Input
→
371
HBW Equivalent
→
390
HV Equivalent
Tensile Strength
1,280 MPa
Standard
ASTM E140
Accuracy
±5%
Why Material Family Matters
①
Carbon & Alloy Steel
Most conversion tables are calibrated for carbon steel. Applies to 4140, 4340, D2, and similar alloys. ±5% accuracy.
HBW ≈ 3.45 × UTS (MPa)
②
Austenitic Stainless
Stainless steels work-harden during testing. Conversion curves are different from carbon steel. ±10% accuracy.
Use separate tables per ASTM E140
③
Aluminum, Brass, Copper
Non-ferrous metals have very different elastic-plastic responses. A 95 HBW reading on aluminum equals ~60 HRB, not the steel equivalent of ~50 HRB.
Material-specific tables requiredHow Each Hardness Scale Works
Rockwell (HRC / HRB / HRA)
Measures indentation depth under load. HRC uses a diamond cone at 150 kg for hardened steels. HRB uses a steel ball at 100 kg for softer metals. Fast production-line QC.
Brinell (HBW)
Measures the diameter of a large ball indentation. The wide footprint averages microstructural variation in castings and forgings. Preferred for inhomogeneous materials.
Vickers (HV) & Knoop (HK)
Uses a diamond pyramid at low loads. Vickers is universal across all metals. Knoop has an elongated indenter for coatings, weld zones, and thin layers where Vickers spans too wide.
CNC MACHINING IMPACT
How Hardness Affects CNC Machining
Hardness is not just a number on an MTR; it directly determines how a material machines. As hardness increases, machinability decreases. Feeds and speeds must be dialed back, tool life shortens, and part cost shifts.
A practical comparison across the hardness spectrum, using materials Baetro machines daily. From annealed aluminum at 30 HBW to hardened D2 at 62 HRC, the machining strategy changes completely. Baetro covers the full range across 50+ materials with 5-axis simultaneous machining capability.
Low Hardness (Excellent Machinability)
Aluminum alloys (~95 HBW), 1018 mild steel (~120 HBW), and C360 brass (~80 HBW) machine at high speeds with excellent tool life and surface finish.
- High cutting speeds
- Long tool life
- Low cost per part
Moderate Hardness (Fair Machinability)
304 stainless (~30 HRC), 4140 hardened (~32–43 HRC), and Ti-6Al-4V titanium (~30–40 HRC) require carbide tooling, lower speeds, and flood coolant.
- Carbide tooling mandatory
- Reduced cutting speeds
- Work-hardening risk
High Hardness (Poor Machinability)
D2 tool steel (~55–62 HRC) approaches the practical limit of conventional machining. Fine features typically require EDM or grinding. Hard-turning and hard-milling strategies are specialized.
- EDM or grinding required
- Specialized tooling
- Higher machining cost
Machine Your Part in Any Hardness
Baetro machines 50+ materials from annealed aluminum to hardened D2. Get free DFM feedback on hardness callouts that may be tighter than the part needs.
Common CNC Material Hardness Reference
Engineers and inspectors use this table as a sanity check: does the hardness on the drawing match what is reasonable for the material?
| Material | Hardness (Typical) | Tensile Strength (Approx.) | Common Condition |
|---|---|---|---|
| 6061-T6 Aluminum | ~95 HBW / ~60 HRB | ~310 MPa / ~45 ksi | Solution heat-treated and aged |
| 7075-T6 Aluminum | ~150 HBW / ~87 HRB | ~570 MPa / ~83 ksi | Solution heat-treated and aged |
| 1018 Mild Steel | ~120–200 HBW / ~70–95 HRB | ~400–650 MPa | Hot-rolled or cold-drawn |
| 304 Stainless Steel | ~150–300 HBW / ~80 HRB–32 HRC | ~515–860 MPa | Annealed to strain-hardened |
| 316 Stainless Steel | ~150–280 HBW / ~80 HRB–28 HRC | ~515–790 MPa | Annealed |
| 4140 Alloy Steel | ~200 HBW / ~15 HRC (annealed) | ~655 MPa | Annealed |
| 4140 Alloy Steel | ~300–400 HBW / ~32–43 HRC (hardened) | ~1,000–1,380 MPa | Quenched and tempered |
| A2 Tool Steel | ~60 HRC / ~700 HV | ~2,070 MPa | Hardened and tempered |
| D2 Tool Steel | ~55–62 HRC / ~600–750 HV | ~1,900–2,200 MPa | Hardened and tempered |
| Ti-6Al-4V | ~30–40 HRC / ~300–380 HV | ~900–1,100 MPa | Annealed |
| C360 Brass | ~80 HBW / ~55 HRB | ~350 MPa | Half-hard |
Browse our materials → for full property data sheets
HARDNESS CONVERSION FAQS
Hardness Conversion FAQs
Hardness conversion translates a material’s measured hardness between different test scales (Rockwell HRC, Brinell HBW, Vickers HV) using empirical correlation tables per ASTM E140 and ISO 18265. There is no exact mathematical formula; conversions are based on paired measurements of reference test blocks.
Use the ASTM E140 conversion table for the specific material family. For carbon and low-alloy steels: 20 HRC ≈ 229 HBW, 30 HRC ≈ 286 HBW, 40 HRC ≈ 371 HBW, 50 HRC ≈ 481 HBW, 60 HRC ≈ 620 HBW. This calculator automates the lookup with material-family-aware table selection.
Approximately ±5% for carbon and low-alloy steels within the 20–68 HRC range per ASTM E140. Accuracy drops to ±10–15% at the extremes and for non-ferrous materials. Conversions should never replace direct measurement for final acceptance or certification.
Rockwell measures indentation depth — fast production-line QC. Brinell measures indentation diameter optically with a large indenter — preferred for castings and forgings. Vickers measures diagonals of a microscopic diamond-pyramid indentation — universal across all metals and usable on thin layers.
Each material family has a different elastic-plastic response. A 95 HBW measurement on carbon steel corresponds to ~50 HRB, but the same 95 HBW on 6061-T6 aluminum corresponds to ~60 HRB. Applying a steel conversion table to a non-ferrous material produces errors of 10% or more.
For carbon and low-alloy steels, approximate UTS (MPa) ≈ 3.45 × HBW, per ASTM A370. This relationship breaks down for austenitic stainless steels, aluminum alloys, and highly alloyed tool steels. Use the estimate for reference only; never derive a material certification UTS from a hardness conversion.
NACE MR0175 / ISO 15156 limits carbon and low-alloy steels in H₂S-containing environments to 248 HV maximum (approximately 22 HRC). General structural welding codes (AWS D1.1) limit hardness to 350 HV (approximately 36 HRC) for non-sour service. Always verify by direct measurement on the specified scale.
Hardened steels (above ~20 HRC): Rockwell C. Softer steels, brass, aluminum: Rockwell B or Brinell. Thin sheets, coatings: Vickers (HV) or Knoop (HK). Castings, forgings: Brinell. Elastomers and plastics: Shore durometer; not convertible to metal scales.
No. Shore measures elastic recovery in polymers and elastomers; Rockwell/Brinell/Vickers measure plastic deformation in metals. The measurement physics are fundamentally different, and no valid correlation table exists between them. If a specification calls out a Shore value, the material is almost certainly a polymer.
Machinability decreases as hardness increases. At low hardness, cutting speeds are high and tool life is long. At moderate hardness, carbide tooling becomes mandatory. At high hardness, conventional machining reaches its practical limit; fine features typically require EDM or grinding. The calculator’s material reference table maps common materials to their typical machining behavior.
FROM MATERIAL SPEC TO CERTIFIED PART
From Hardness Spec to Machined Part
You have a hardness value converted across every relevant scale. Now you need the part that delivers it — machined from the exact alloy your drawing specifies, with hardness verified against the callout, and full traceability back to the mill. Baetro stocks 50+ materials and ships with full MTR documentation and CMM inspection reports.
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50+ materials in stock
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Full MTR & hardness traceability
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