Hardness conversion chart: HRC, HB, HV and tensile strength.
A test certificate quotes 45 HRC, your drawing calls out 430 HB, and the customer asks for the tensile strength. All three describe the same steel. Here is how the Rockwell, Brinell and Vickers scales relate, why every conversion is an approximation, and a worked example you can trust on the shop floor.
The hardness scales you will meet
Hardness is resistance to localised plastic deformation. Each scale measures it with a different indenter and load, so each produces its own number:
- Rockwell C (HRC) — a 120° diamond cone under a 150 kgf load. The default for hardened steel, roughly 20–70 HRC.
- Rockwell B (HRB) — a 1.588 mm ball under 100 kgf. Used for softer steels, brass and aluminium alloys.
- Brinell (HB / HBW) — a 10 mm tungsten-carbide ball, usually 3000 kgf for steel. The large indent averages over a big area, so it suits castings and coarse-grained material.
- Vickers (HV) — a square-based diamond pyramid, any load from grams to 100 kgf. One continuous scale from soft foil to the hardest steel, ideal for thin sections and case depth.
Why conversion is always approximate
There is no exact physical law linking the scales. Each indenter deforms the metal differently, so conversions come from empirical correlation tables, principally ASTM E140 and ISO 18265. Those tables were built mostly from non-austenitic steels. Apply them to stainless, non-ferrous metals or work-hardened surfaces and the error grows quickly.
Conversion chart for steel
Approximate equivalents for carbon and low-alloy steel, consistent with ASTM E140. Use the MetricMech hardness conversion calculator for any value in between — it interpolates the full table for HRC, HRB, HB, HV and Shore.
| HRC | HV | HB | HRB | Tensile (MPa) |
|---|---|---|---|---|
| 60 | 697 | — | — | 2240 |
| 55 | 595 | — | — | 2075 |
| 50 | 513 | 481 | — | 1740 |
| 45 | 446 | 421 | — | 1480 |
| 40 | 392 | 371 | — | 1290 |
| 35 | 345 | 327 | — | 1120 |
| 30 | 302 | 286 | — | 965 |
| 25 | 266 | 253 | — | 850 |
| 20 | 238 | 226 | 98 | 770 |
| — | 200 | 190 | 92 | 650 |
| — | 170 | 162 | 85 | 550 |
Dashes mark regions where a scale is out of its valid range — HRC below about 20 and Brinell above about 480 HB are unreliable, which is exactly why those bands are left blank on a good chart.
Hardness to tensile strength
For carbon and low-alloy steel there is a useful rule of thumb: tensile strength in MPa is approximately 3.4 × HB. A part at 200 HB is therefore around 680 MPa. This estimate underpins many incoming-material checks — a quick hardness test substitutes for a destructive tensile test. It does not hold for non-ferrous metals, austenitic stainless, or heavily cold-worked material.
Worked example
An incoming batch of EN8 (080M40) shaft stock has a mill certificate quoting 250 HB. Your drawing specifies the property as tensile strength, minimum 800 MPa, and your hardness tester only reads Rockwell C.
- Estimate tensile from Brinell: 3.4 × 250 = 850 MPa — above the 800 MPa minimum, so the material looks compliant.
- Find the equivalent HRC to spot-check: 250 HB sits just under the 253 HB / 25 HRC row, so expect roughly 24–25 HRC on your tester.
- Measure and compare: if your Rockwell reading lands near 24–25 HRC, the certificate is consistent. A reading of 18 HRC would flag a mix-up or a soft batch worth investigating before machining.
This is the everyday value of conversion: cross-checking a certificate against the instrument you actually own, without scrapping a sample for a tensile test.
Which scale should you specify?
| Situation | Best scale | Why |
|---|---|---|
| Hardened steel, >20 HRC | HRC | Direct, fast, repeatable |
| Soft steel, brass, aluminium | HRB or HB | HRC indenter would punch through |
| Castings, large sections | HB | Large indent averages coarse grain |
| Thin sheet, coatings, case depth | HV | Light loads, tiny indent |
Specifying the scale that matches the material and section avoids the conversion problem entirely. If you also control surface texture on the same feature, our Ra vs Rz guide covers how those callouts interact with hardened surfaces.
Frequently asked questions
Is hardness conversion accurate?
Conversions are approximations valid mainly for non-austenitic steels per ASTM E140. Because there is no exact relationship between scales, converted values can differ by several points. For acceptance, always measure on the scale the drawing specifies.
How do I convert HRC to HB?
Use an ASTM E140 table or a calculator. As a rough guide for steel, 20 HRC ≈ 226 HB, 30 HRC ≈ 286 HB, 40 HRC ≈ 371 HB, and 50 HRC ≈ 481 HB. Above about 450 HB the Brinell scale becomes unreliable, so switch to Rockwell C or Vickers.
What links hardness and tensile strength?
For steel, tensile strength in MPa is roughly 3.4 × the Brinell number, so 200 HB ≈ 680 MPa. It is an estimate for carbon and low-alloy steels only and does not apply to non-ferrous metals.