Hardness Scale Converter (HV, HB, HRC, HRB, Knoop)
Hardness Scale Converter (HV, HB, HRC, HRB, Knoop)
Vickers, Brinell, Rockwell C and B and Knoop for non-austenitic steel — and a refusal for the other six material groups ASTM E140 gives separate tables to, because there is no universal hardness conversion. Each scale’s valid range is enforced and the blank outside it is the answer. Shore A and Shore D do not convert to metal scales at all.
Hardness scales, per material group
380 HBW 10/3000 on a non-austenitic steel
Definitions that are geometry, conversions that are a convention
- 1.8544
- 2 sin 68°, from the Vickers pyramid’s 136° included angle. Not a fitted constant — pure geometry, and the reason HV is load-independent above about 200 gf
- 14.229
- the reciprocal of the projected-area coefficient of the Knoop indenter’s 172.5° and 130° angles. Also pure geometry
- F / D²
- the Brinell test’s similarity number. Two Brinell tests are comparable when this matches: 3000/10², 750/5² and 187.5/2.5² are all 30, and are the same test at three sizes
- h
- the permanent depth increase, in mm. One Rockwell point is two microns of it — which is why Rockwell is not load-independent and Vickers is
- 3.45
- the tensile rule, and the chart this page uses puts it against VICKERS, not Brinell. On hardened steel the Brinell coefficient is nearer 3.66. It is an estimate for steels only and no substitute for a tensile test
- the material group
- required. ASTM E140 has seven tables and says its values are valid only for the material named. This page has one of them
Worked example
380 HBW 10/3000 on a non-austenitic steel
380 HB sits between the chart's 371 and 390 rows, so Vickers interpolates to 401.5 HV — and HB ÷ HV here is 0.9465, the 0.94 the chart uses throughout its hardened half
Rockwell C comes out at 40.9 HRC, comfortably inside the 20 to 70 the scale is valid over
Rockwell B is blank: this steel is far above HRB 100, where the 1.588 mm ball flattens against the work. That blank is the answer, not a failure
The tensile estimate at 3.45 × HV is 1,385 MPa. The other published form, 500 psi × HB, gives 1,310 MPa — 5.7% apart, even though the two coefficients are the same number (500 psi is 3.4474 MPa). They differ because one is applied to Vickers and the other to Brinell
Change the material to anything but non-austenitic steel and every row above goes blank. ASTM E140 has a separate table for each group and this page carries one of them
ASTM E140 publishes SEVEN tables, not one
| Material group | Does this page convert it? |
|---|---|
| Non-austenitic steels — carbon, alloy and tool steels, as-forged, annealed, normalised or quenched and tempered | Yes. This is the one table this page carries, from a named secondary chart. |
| Nickel and high-nickel alloys (over 50% Ni) | No. E140 has its own table for it and this page does not have the numbers. |
| Cartridge brass | No, for the same reason. |
| Austenitic stainless steel | No. Austenitic stainless work-hardens under the indenter, so its conversions differ from a carbon steel’s at the same hardness by more than any sensible tolerance. |
| Copper | No. |
| Alloyed white cast iron | No. |
| Wrought aluminium products | No. |
| Elastomers and plastics (Shore A, Shore D) | No, and not because of a missing table — there is no relation to convert. See below. |
A bare “HB” number is incomplete
| Notation | Ball D (mm) | Force F (kgf) | F ÷ D² | Force (N) |
|---|---|---|---|---|
| HBW 10/3000 — 10 mm ball, 3000 kgf | 10.0 | 3,000.0 | 30.0 | 29,420 |
| HBW 10/1500 — 10 mm ball, 1500 kgf | 10.0 | 1,500.0 | 15.0 | 14,710 |
| HBW 10/500 — 10 mm ball, 500 kgf | 10.0 | 500.0 | 5.0 | 4,903 |
| HBW 5/750 — 5 mm ball, 750 kgf | 5.0 | 750.0 | 30.0 | 7,355 |
| HBW 2.5/187.5 — 2.5 mm ball, 187.5 kgf | 2.5 | 187.5 | 30.0 | 1,839 |
| HBW 1/30 — 1 mm ball, 30 kgf | 1.0 | 30.0 | 30.0 | 294 |
What the published chart says about itself
| Check | Result | What it means |
|---|---|---|
| HB ÷ HV across the 20 hardened rows that have both | 0.9410, every row within 1.6% of it | A tight, near-constant ratio. Brinell and Vickers are different tests, so a constant ratio between them over 400 points of hardness is a sign the column was generated rather than measured. |
| HB ÷ HV across the 21 softer rows | exactly 1.000, in every row | The chart’s soft half sets Brinell EQUAL to Vickers. That cannot be a measurement either, and it contradicts the hard half by 6.3%. |
| The two halves at the HRC 20 row they share | HV 244 / HB 226 in one, HV 228 / HB 228 in the other | A 7.0% disagreement inside one chart, at the row where its two tables meet. Stitch them and the Brinell column falls by 14 points as Vickers rises by 4. This page therefore does NOT stitch them: it keeps the two tables separate and leaves HV 240 to 244 blank. |
| ISO 18265’s own HB ÷ HV, from two published endpoints | 0.95 | A third relation again, between the same two scales, in a standard. Three published answers to one question. |
| Tensile ÷ HV across the 22 hardened rows with a tensile figure | 3.4452, varying by 0.67% at most | So the famous 3.45 coefficient belongs to VICKERS, and in this chart it is a generated column rather than measured scatter. |
| Tensile ÷ HV across the softer rows | 3.4375 | The same coefficient, confirming it. |
| Tensile ÷ BRINELL across the hardened rows | 3.6614 | Which is 6.1% above 3.45. Applying “3.45 × HB” to hardened steel understates the tensile strength by about that much, because the constant was never a Brinell constant. |
| Tensile ÷ Brinell across the whole chart, both halves | 3.409 to 3.702 | A 8.6% spread. That is the scatter in the tensile rule, and it is structural rather than random: the ratio rises with hardness. |
| Rockwell C values the chart prints in its soft table | down to HRC 2 | Below the scale’s own 20 HRC floor. This page returns nothing below 20 HRC rather than printing a number the test cannot produce. |
Where each scale is valid, and what happens outside it
| Scale | Indenter and load | Valid range | What this page does outside it |
|---|---|---|---|
| Vickers HV | 136° diamond pyramid, any load above about 200 gf | One continuous scale, roughly 5 to 2400 HV | Nothing to enforce. Vickers is load-independent above about 200 gf and that is why this page uses it as the pivot: HV 500 from a 500 gf test and from a 50 kgf test are the same number. Below 200 gf the indentation size effect appears and the number starts to depend on the load. |
| Brinell HBW | 10 mm tungsten carbide ball, 3000 kgf (or a geometrically similar pair) | Up to 650 HBW (ISO 6506-1) | Returns nothing above 650. The carbide ball deforms against a harder material and the measurement stops meaning anything. |
| Rockwell C HRC | 120° diamond cone, 150 kgf major load over a 10 kgf preload | 20 to 70 HRC | Returns nothing below 20 HRC. Rockwell C is NOT load-independent — it measures a depth, and at low hardness the indentation is too deep for the scale to resolve. Use HRB there. |
| Rockwell B HRB | 1.588 mm ball, 100 kgf major load | 20 to 100 HRB | Returns nothing above 100 HRB. Above it the ball flattens against the work and the reading compresses. Use HRC there. |
| Knoop HK | Elongated diamond pyramid, 172.5° and 130°, typically 0.01 to 1 kgf | A microhardness scale | Given only in the hardened range, where the chart carries it. Knoop is for thin coatings, brittle materials and hardness traverses across a case, and its shallow elongated indentation is more load-sensitive than Vickers. |
| Shore A and Shore D | Spring-loaded indenter on a durometer, elastomers and plastics | Shore A 30 to 95, Shore D 40 to 90 | Refused entirely. See the note below. |
Shore A and Shore D do not convert to metal scales at all
| Metal hardness scales | Shore durometer scales | |
|---|---|---|
| What is measured | The size or depth of a PERMANENT plastic indentation left after the load is removed | The depth an indenter reaches against a calibrated spring while the load is applied — and an elastomer springs back |
| The material’s response | Plastic flow. The indentation stays | Almost entirely elastic. The indentation largely disappears |
| What the number tracks | Resistance to plastic deformation, which is why it correlates with yield and tensile strength | Elastic modulus and recovery, which do not |
| Scale | Open-ended (HV to 2400 and beyond) | 0 to 100 by construction, against a spring |
| Can it be converted? | Between metal scales, approximately and per material group | No. Not approximately, not per material group, not at all. |
Seven tables, not one, and the blank is the answer
ASTM E140 is the standard for hardness conversion, and its central fact is that it publishes seven tables rather than one. Separate conversions for non-austenitic steels, for nickel and high-nickel alloys, for cartridge brass, for austenitic stainless steel, for copper, for alloyed white cast iron and for wrought aluminium. Its own scope says the values “should only be considered valid for the specific materials indicated”, that conversion between scales “is only an approximate process”, and that it should be avoided “whenever possible”. There is no universal hardness conversion. That is why the material select on this page is required and why it refuses six of the seven groups outright: this page has the non-austenitic steel table and it does not have the others, and a number from the wrong table is worse than no number at all.
The definitions are geometry. Only the conversions are a convention. A Vickers number is 1.8544 F/d² with the force in kilograms-force, and that 1.8544 is 2 sin 68°, straight out of the indenter’s 136° included angle. Knoop’s 14.229 is the reciprocal of the projected-area coefficient of its 172.5° and 130° pyramid. Brinell is 2F/(πD(D − √(D² − d²))), the load over the curved area of the impression. Rockwell is simpler still: HRC = 100 − h/0.002 mm, so one Rockwell point is two microns of permanent depth and the whole 20-to-70 range is a tenth of a millimetre. Every one of those is computable and none of them needs a table. What needs a table is the relation BETWEEN them, because that depends on how the particular material flows under the particular indenter.
Vickers is load-independent and Rockwell is not, which is why this page pivots on Vickers. A Vickers indentation is geometrically similar at any load, so HV 500 measured at 500 gf and at 50 kgf is the same number — as long as the force is at least about 200 gf, below which the indentation size effect appears. Rockwell measures a depth at one fixed load per scale, so its number belongs to its apparatus. And both Rockwell scales have hard ends: Rockwell C is invalid below about 20 HRC because the cone sinks too deep to resolve, and Rockwell B above about 100 HRB because the ball flattens against the work. This page returns nothing outside those ranges rather than extrapolating. The blank is the honest answer, and a chart that prints “HRC 2” — as the source chart for this page does, nine times — is printing a number no Rockwell C test could produce.
A Brinell number without its test conditions is incomplete. HBW 10/3000 is a 10 mm tungsten carbide ball at 3000 kgf. What makes two Brinell tests comparable is the ratio F/D², because similar indentations give the same number: HBW 10/3000, HBW 5/750 and HBW 2.5/187.5 are all F/D² = 30, the same test at three sizes, and that is how you test something thin or small. HBW 10/1500 and HBW 10/500 are F/D² of 15 and 5, different tests whose numbers do not interchange with the 3000 kgf ones. Brinell also has a ceiling of 650 HBW in ISO 6506-1, above which the carbide ball itself deforms — so no Brinell figure appears above it here.
The tensile estimate is the most-searched part, and it is misattributed. The rule everyone quotes is that tensile strength in MPa is about 3.45 times the hardness, or 500 psi times it. Those two are the same coefficient: 500 psi is 3.4474 MPa, agreeing with 3.45 to 0.08%. But the chart this page uses puts that coefficient against Vickers, not Brinell — its tensile column is 3.445 × HV, constant to within 0.7% over twenty-two rows, which is a generated column rather than measured data. Against Brinell on hardened steel the same chart implies 3.661, because it sets HB at 0.94 × HV there. So “3.45 × HB” understates a hardened steel’s tensile strength by about six per cent, and the scatter across the whole chart runs from 3.41 to 3.70 — a 9% spread that rises systematically with hardness. It applies to steels only, and it is an estimate: a tensile test measures a different thing under different constraint, and no hardness number contains the ductility, the yield ratio or the toughness.
What the source chart says about itself is the most useful thing on this page. E140 is copyrighted and was not reproduced here; the steel values come from a named secondary chart that credits E140 and ISO 18265, and it could not be checked against the standard. So instead this page checks it against itself, and the results are instructive. Its hardened half puts Brinell at 0.94 × Vickers, within 1.6% in every one of twenty rows. Its softer half puts Brinell EQUAL to Vickers, in all twenty-one. At the one row where the two halves meet, HRC 20, one gives HV 244 and HB 226 and the other HV 228 and HB 228 — a seven per cent disagreement inside a single chart. ISO 18265, through a second secondary source, uses 0.95 throughout: a third answer to the same question. A chart whose two halves use incompatible relations between the same two scales is not reporting measurements, it is reporting a convention — which is exactly what E140 says a hardness conversion is. This page therefore keeps the two halves apart, leaves the four points between them blank, and tells you which half your answer came from. For the other property that does not really convert either, see the surface roughness converter; for the fluid properties on the same machine, the viscosity converter and the density and specific gravity converter.
Frequently asked questions
Is there a universal hardness conversion chart?
No, and ASTM E140 — the standard for hardness conversion — says so by its own structure: it publishes SEVEN separate tables, for non-austenitic steels, nickel and high-nickel alloys, cartridge brass, austenitic stainless steel, copper, alloyed white cast iron and wrought aluminium. Its scope states that the values “should only be considered valid for the specific materials indicated”, that conversion “is only an approximate process”, and that it should be avoided “whenever possible”. The reason is physical: a conversion depends on how the material work-hardens and on its elastic modulus, so two materials at the same Vickers hardness give different Rockwell numbers. This page carries one table and refuses the rest.
What does HBW 10/3000 mean, and is a bare HB number enough?
It means a tungsten carbide ball (the W), 10 mm in diameter, pressed at 3000 kgf. A bare “HB” is not enough, because the number depends on those conditions. What makes two Brinell tests comparable is the ratio F/D²: 3000/10², 750/5² and 187.5/2.5² are all 30, so those three are the same test at three sizes and you pick the small one for a small or thin part. HBW 10/1500 is F/D² = 15 and HBW 10/500 is 5, and their numbers are not interchangeable with the 3000 kgf ones. The older HBS notation meant a hardened steel ball, which ISO 6506 no longer permits.
Is tensile strength really 3.45 times the Brinell hardness?
It is about 3.45 times the VICKERS hardness, and that is a distinction worth having. The chart this page uses implies 3.445 against HV — constant to within 0.7% over twenty-two rows, which is a generated column rather than measured scatter — and 3.661 against Brinell on hardened steel, because in that chart HB is 0.94 × HV. Across the whole chart the tensile-to-Brinell ratio runs from 3.41 to 3.70, a 9% spread that rises with hardness. The two published forms, 3.45 MPa and 500 psi per point, are the same coefficient — 500 psi is 3.4474 MPa, agreeing to 0.08% — so where they disagree in practice it is because sources apply them to different scales. It applies to steels only and it is an estimate, never a substitute for a tensile test.
Why is Rockwell C blank below 20 HRC?
Because the measurement is invalid there, and a blank is the honest answer. Rockwell C measures a permanent indentation DEPTH — HRC = 100 − h/0.002 mm, so one point is two microns — and on a soft material the diamond cone sinks too far for the scale to resolve. Its published range is 20 to 70 HRC. Rockwell B has the mirror problem above 100 HRB, where the 1.588 mm ball flattens against the work. This page returns nothing outside either range rather than extrapolating, and there is a small gap between them where neither is offered. That gap is also where the source chart’s two halves contradict each other, so filling it in would be inventing.
Why does this page work through Vickers?
Because Vickers is the only one of these scales that is load independent over a useful range. The Vickers number is 1.8544 F/d², straight out of the 136° pyramid’s geometry, and a geometrically similar indentation gives the same number whatever the load — the same HV from 500 gf and from 50 kgf, as long as the force is at least about 200 gf. Rockwell is not like that: it measures a depth at one fixed load per scale, so its number is tied to its apparatus. Pivoting on the scale that is a property of the material rather than of the machine is the only defensible way to route between the others.
Can I convert Shore A or Shore D to Vickers or Brinell?
No, and this is a refusal rather than a missing table. A durometer measures how far a spring-loaded indenter sinks into a rubber WHILE it is pressed, and the rubber pushes back; a Vickers or Brinell test measures the permanent hole left in a metal after the load comes off. The first is dominated by elastic modulus and recovery, the second by plastic flow. There is no quantity common to both for a conversion to be about. Shore A and Shore D do not convert reliably to each other either, which is why hard rubbers are often quoted in both.
Why does austenitic stainless need its own table?
Because it work-hardens heavily under the indenter. The plastic zone round a Vickers or Brinell impression in 304 or 316 gets substantially harder than the bulk material as it deforms, which changes the relationship between the indentation a diamond cone leaves and the one a ball leaves — and those are the two instruments you are trying to relate. ASTM E140 therefore gives austenitic stainless its own conversion table, separate from the non-austenitic steels. Using a carbon-steel chart on stainless is one of the commonest ways to get a hardness conversion badly wrong, and this page will not do it.
Should I be converting at all?
Probably not, if you have a choice. ASTM E140’s own advice is to avoid conversions “whenever possible” and to apply them to specification limits rather than to test data. Test on the scale the specification is written in. Where a conversion is unavoidable — a certificate in Brinell against a drawing in Rockwell — treat it as carrying a few points of uncertainty, say in the report that the figure is converted and on what table, and never quote a converted value to more precision than the conversion deserves. For surface finish, which has the same problem of parameters that do not really convert, see the surface roughness converter.
Related calculators
References
- ASTM E140, Standard Hardness Conversion Tables for Metals: Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness. Copyrighted and not fetched; ASTM’s own published scope was, and it is the reason this page exists. It names SEVEN separate material groups — non-austenitic steels, nickel and high-nickel alloys, cartridge brass, austenitic stainless steel, copper, alloyed white iron and wrought aluminium — and states that “the conversion values given in the tables … should only be considered valid for the specific materials indicated”, that “conversion from one hardness scale to another is only an approximate process”, and that conversions should be avoided “whenever possible”.
- metricmech.com. Hardness Conversion Chart: Rockwell, Brinell, Vickers, Knoop. The anchor table this page interpolates, credited there to ASTM E140 and ISO 18265 and restricted there to “through-hardened or case-hardened carbon and alloy steels, HRC 20–65” and, for its second table, to unhardened and low-carbon steel at HRB 60–100. It is a secondary source and it could not be checked against the standard, so what this page reports instead is what the chart says about ITSELF: its hard half puts HB at 0.941 × HV, its soft half puts HB EQUAL to HV in all 21 rows, the two halves disagree by 7% at the HRC 20 row they share, and its tensile column is 3.445 × HV to within 0.7% over 22 rows — a generated column, not a measured one.
- stahlportal.com. Hardness comparison table. Based on DIN EN ISO 18265 for “unalloyed and low-alloy steels”, running from 80 HV / 76.0 HB / 255 N·mm⁻² to 650 HV / 618 HB / 2180 N·mm⁻², and giving the validity limits 20 to 100 HRB and 20 to 70 HRC. Both of its endpoints put HB at exactly 0.95 × HV, which is a THIRD relation between the same two scales.
- ISO 18265, Metallic materials — Conversion of hardness values. Cited by number through the two secondary sources above; not fetched.
- ISO 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method, and ISO 6507-1 for Vickers. Cited by number. The definitions this page computes from are geometric and were verified from the indenter geometry rather than quoted: the Vickers constant 1.8544 is 2 sin 68°, the Knoop constant 14.229 is the reciprocal of the projected-area coefficient of a 172.5°/130° pyramid, and HBW’s 650 ceiling is the Brinell standard’s own limit for a tungsten carbide ball.
- AIMS Industrial. Hardness Testing Guide: Rockwell, Brinell, Vickers & Knoop. aimsindustrial.com. Scale ranges (20–70 HRC, 20–100 HRB, Vickers one continuous scale, Knoop 0.01–1 kgf, Shore A 30–95 and Shore D 40–90), the loads and indenters of each test, and the instruction that matters most here: “Do not convert across material families.”
- Wikipedia, Vickers hardness test. Used for one quantitative claim only, the load-independence threshold: “Vickers values are generally independent of the test force … as long as the force is at least 200 gf.” Below that the indentation size effect appears, which is the reason Vickers is the scale this page pivots on and Rockwell is not.
- Metkon. Hardness Conversion Table (Chart) and What is the Vickers Hardness Test? metkon.com. Publishes both forms of the tensile rule side by side — “Tensile Strength (MPa) ≈ 3.45 × Brinell Hardness” and “Tensile Strength (psi) ≈ 500 × Brinell Hardness” — which is where this page’s comparison of the two starts.