ASTM E140 · non-austenitic steels

Hardness conversion calculator

Free and no signup: enter one hardness reading and the other four scales — Rockwell C, Rockwell B, Brinell, Vickers and approximate tensile strength — come back together, read out of the ASTM E140 anchor rows for carbon and alloy steel. Twenty-three of that table’s 95 cells are empty, and this page leaves them empty: no Brinell above HRC 65, no tensile above HRC 50, no Rockwell B above HRC 20. Every figure it does return is a converted value rather than a tested one, and it says so beside the number.

100% free
No signup
5 scales, 20 directions
ASTM E140 Table 2
Prints as one sheet

The reading you have

One number in, the other four scales out. Which material it is decides whether there is a conversion to make at all.

What was tested

Five of these six stop the conversion. That is the point of asking.

Scale it was measured on

Reading

20 to 68. 150 kgf on a 120° diamond cone (ASTM E18). Reads the permanent depth of the indent, so a higher number is a shallower dent.

Tensile per Brinell point, for the shop rule

Default 500 psi per Brinell point. The long-standing approximation for carbon and alloy steels, tensile (psi) ≈ 500 × HB. Checked against the E140 anchor rows above it is 3–6% high through HB 226–371 (226 → 113 ksi against 107; 371 → 186 against 182) and falls below the table above HB 450. Steels only, and only in the annealed-to-moderately-hardened range, roughly HB 150–400. Not valid for austenitic stainless, cast iron, or any non-ferrous metal. Where the table above has a tensile value, prefer it.

Measured

HRC 45

Rockwell C

Converted, not tested

Every figure below is read across a correlation table. On a certificate or a drawing it is written as a converted value with the scale it was converted from, never as a test result.

Rockwell C 45 on every other scale this table carries
Rockwell B	no value in the tableAbove HRC 20 the Rockwell B column is empty — the last row carrying both is HRB 100. Above HRB 100 the steel ball begins to flatten and the reading stops being repeatable — that is where the C scale takes over. Below HRB 60 accuracy falls away and the E or F scales are used.
Brinell	HB 421Printed row of the table at HRC 45.
Vickers	HV 446Printed row of the table at HRC 45.
Tensile strength (approx.)	213 ksi · 1,469 MPaPrinted row of the table at HRC 45.

The 500 x HB shop rule, checked

421 HB at 500 psi per Brinell point gives 211 ksi · 1,451 MPa, which is 1.2% below the 213 ksi · 1,469 MPa the table itself carries here.

ASTM E140, Standard Hardness Conversion Tables for Metals, Table 2 — non-austenitic steels (carbon and alloy steels in the hardened, tempered, normalized or annealed condition). Brinell values are for a 10 mm ball at 3000 kgf. Approximate tensile strengths correspond to the values SAE J417 and E140 publish alongside the hardness columns. Approximate, material-dependent and not valid across all ranges — see the HardnessRow group docstring, which is not boilerplate. In short: these are for non-austenitic steels only; Rockwell C below 20 and Rockwell B above 100 are outside their scales; Brinell above about 650 exceeds what a standard ball can measure; and the conversion is not reversible. Anything between the anchor rows is linear interpolation, not a printed E140 value, and carries perhaps a point or two of extra error on top of the several points inherent in the conversion itself.

The ASTM E140 anchor rows

Nineteen rows, hardest first, exactly as the columns are printed — no cell filled in to make the grid look complete. Print this page and the chart comes out on its own sheet.

ASTM E140 Table 2 anchor values for non-austenitic steels: Rockwell C, Rockwell B, Brinell, Vickers and approximate tensile strength
Rockwell C	Rockwell B	Brinell	Vickers	Tensile, ksi	Tensile, MPa
68	—	—	940	—	—
65	—	739	832	—	—
60	—	654	697	—	—
55	—	560	595	—	—
50	—	481	513	256	1,765
45	—	421	446	213	1,469
40	—	371	392	182	1,255
35	—	327	345	159	1,096
30	—	286	302	138	951
25	—	253	266	122	841
20	100	226	238	107	738
—	95	210	210	102	703
—	90	185	185	90	621
—	85	165	164	81	558
—	80	150	150	74	510
—	75	137	137	68	469
—	70	125	125	63	434
—	65	115	115	59	407
—	60	107	107	56	386

— is an empty cell in the standard, not a rounding. Brinell against a 10 mm ball at 3,000 kgf; Vickers under a 136° diamond pyramid. ASTM E140, Standard Hardness Conversion Tables for Metals, Table 2 — non-austenitic steels (carbon and alloy steels in the hardened, tempered, normalized or annealed condition). Brinell values are for a 10 mm ball at 3000 kgf. Approximate tensile strengths correspond to the values SAE J417 and E140 publish alongside the hardness columns.

How to convert a hardness reading without inventing one

Three steps, and the second is the one that decides whether the third means anything.

Say what the metal is
Pick the material class first, because it decides whether a conversion exists at all. The page opens on carbon and alloy steel, which is the class ASTM E140 Table 2 was measured on; the other five settings stop the calculation and name the instrument that should have been used instead.
Enter the reading on the scale it was taken on
Choose Rockwell C, Rockwell B, Brinell, Vickers or approximate tensile, then type the figure the machine gave you. Each scale carries its own accepted range — HRC 20 to 68, HRB 60 to 100, HB 107 to 650, HV 107 to 940 — and a reading outside it comes back refused with the reason rather than converted anyway.
Read the empty cells as well as the full ones
Each row states whether it came off a printed anchor row or was interpolated between two named ones, so you can see how far the answer is from something the standard actually published. A row that says there is no value in the table is the answer: the column ends there. Copy the set for a work order, or print the page for the 19-row chart.

Technical specifications

Scales carried	Rockwell C, Rockwell B, Brinell (10 mm ball, 3,000 kgf), Vickers and approximate tensile strength — 20 directions between the five, each read independently rather than inverted from its opposite.
Source table	ASTM E140 Table 2, non-austenitic steels: carbon and alloy steels hardened, tempered, normalized or annealed. 19 anchor rows, hardest HRC 68 / HV 940, softest HRB 60 / HB 107 / HV 107.
Readings accepted	HRC 20–68, HRB 60–100, HB 107–650, HV 107–940, tensile 56–256 ksi (386–1,765 MPa). Anything outside is refused, not clamped.
Cells left empty	23 of the 95. No Rockwell B above HRC 20, no Brinell above HRC 65, no tensile above HRC 50, no Rockwell C below HB 226 — the four places the columns genuinely stop.
Reachable but not enterable	HB 739, opposite HRC 65. The standard prints it and a standard 10 mm ball cannot produce it, so it comes back as an answer and is refused as a question.
Between the anchors	Linear interpolation across the 5-point Rockwell steps, labeled as interpolated and naming both rows it sat between. No answer is more than 2.5 Rockwell points from a printed one.
Material classes offered	Six, of which one converts. Austenitic stainless, cast iron, non-ferrous, case-hardened surfaces and cemented carbide each stop with the reason and the instrument to use instead.
Where it runs	In the browser tab. The reading, the material and the shop-rule figure are never uploaded or stored, and the chart is in the page source rather than fetched.

Frequently asked questions

Why does HRC 68 come back with no Brinell number?

Because a hardened steel ball cannot measure metal that hard. Under 3,000 kgf the ball flattens against the specimen, and the dent that results describes the ball rather than the steel, so the Brinell column of E140 stops at HRC 65 — where it reads 739 HB, already above the 650 this page accepts as a Brinell input. At that hardness the instruments are Vickers or Rockwell C, and the page returns HV 940 while leaving Brinell blank.

Can I put a 304 stainless reading through this?

No, and the material selector stops you. Austenitic grades work-harden under the indenter, so the metal being squeezed by a slow 3,000 kgf ball is not in the same condition as the metal a Rockwell diamond meets, and the correlation between the two instruments comes out different. ASTM E140 measures austenitic stainless on its own table for that reason. Running a 304 number through the carbon-steel columns produces arithmetic about a material you do not have.

Where is the Shore column?

Deliberately absent, because the word means two unrelated instruments. The Shore scleroscope is a rebound test that E140 does correlate against steel hardness, and this site does not reproduce that column — it could not be sourced to the confidence the rest of the table was, so it is left to the standard rather than guessed at. The Shore A and Shore D durometer is a different device altogether, a spring-loaded probe for rubber and plastics, and a durometer reading has no conversion to steel hardness at any number.

Is a converted hardness acceptable on a certificate or a drawing?

Only when it is labeled as converted. ASTM E140 asks that a converted value be reported together with the scale it was converted from — 286 HB (converted from 30 HRC) rather than a bare 286 HB — precisely so that nobody downstream mistakes it for a test. A print calling for 28–32 HRC is met by a Rockwell C test on the part. A Brinell reading that converts neatly into that band is a reason to expect the part will pass, not evidence that it did.

Why doesn't HRC to Brinell and back return the number I started with?

Because the two columns are not evenly spaced against one another. Five Rockwell C points cover 27 Brinell points between HRC 20 and 25, and 85 between HRC 60 and 65, so interpolating one way and then the other lands somewhere else. This page reads the table fresh in each direction instead of inverting its own answer, which makes the round trip visibly lossy rather than invisibly wrong.

Is a number between the printed rows still from the standard?

No, and the page marks it. E140 publishes anchors at 5-point Rockwell steps; anything falling between two of them here is linear interpolation, and the line under the figure names the two rows it sat between. That adds a point or so to an error already several points wide, which is the honest reason every converted figure on this page is labeled converted rather than measured.

What ASTM E140 is, and what it is not

No equation connects Rockwell C to Brinell. E140 is a set of measured correlations — the same specimens tested on several machines, the columns published side by side — which is why the standard’s own language calls conversions approximate and asks that a converted value be reported as converted. The practical consequence is narrow and worth stating plainly: a conversion is for deciding whether to bother testing, for reading a drawing written in a scale your machine does not have, and for talking to a supplier whose certificate is on the other side of the table. It is not for closing out an inspection.

What most converters leave out is the material, and that is the part that actually decides the answer. E140 does not publish one table; it publishes several, because the relationship between two instruments is a property of the alloy family rather than of the instruments. The columns reproduced here are the non-austenitic steel table. Feed a gray iron reading into them and the arithmetic still returns a number — a number about carbon steel, which is not what you measured. That is why the material class here is a field with consequences rather than a sentence in a footnote. The rockwell to brinell page takes the single most-asked pair and works out what the two machines physically do to the steel, which is the shortest route to understanding why a correlation is all there can be.

Downstream, hardness is a stand-in for two other things, and both stand-ins have edges. It stands in for strength: that is the approximate tensile column, and it stops at HRC 50 for a physical reason rather than an editorial one, because above that the steel has lost the ductility to reach the strength its hardness implies and the fitted correlation has ended. And it stands in for machinability, badly — cutting-speed tables are indexed by material and condition, not by a hardness number, which is why the feed and speed calculator asks what the material is rather than how hard it reads. Where hardness does carry directly is into tool life and the finish a cutter can hold, the ground covered by the surface finish chart, and into the surface speed that finish is bought with, which is the axis the surface footage calculator works on.

Where the reading you type goes

Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.

The material class, the scale and the shop-rule figure live in the page’s own memory for as long as the tab is open and are gone when you close it. Nothing is written to storage, so the page always opens on the shipped defaults rather than on somebody else’s last job.