Hardness Conversion Calculator
Hardness Conversion Calculator
Convert between Rockwell C, Rockwell B, Rockwell A, Brinell, Vickers and approximate tensile strength for carbon, low alloy and tool steel. Every result shows the range each scale covers, and says so plainly when your value falls outside it.
The scales lined up on one axis
Values are read from the published steel tables by straight line interpolation between neighboring rows, one HRC or one HRB apart. Tensile strength comes from the table for HRC 20 to 55 and from 3.45 × HBW for softer steel; ksi = MPa ÷ 6.894757. These are approximate conversions for non austenitic steel and never replace a test. The CSV, image and printed report contain the values you entered, nothing preloaded.
How to use this tool
Pick the scale you have, type the reading and the other scales appear with the range each one covers. Rockwell C, Rockwell B, Rockwell A, Brinell, Vickers and tensile strength in MPa or ksi are all accepted as inputs. The two most useful scales appear large, every other scale sits in the cards below with its valid range, and a chart lines all of them up on one axis. If the reading is outside the table, the tool says which limit you passed rather than guessing.
The input people most often get wrong is the Rockwell scale itself. HRC uses a diamond cone at 150 kgf and suits hard steel, and HRB uses a 1/16 inch ball at 100 kgf and suits soft steel. A reading of 95 is a very different steel on each. Brinell is the second trap: enter HBW for the 10 mm ball at 3000 kgf, not the 500 kgf test, which gives different numbers. Everything here is for non austenitic steel, and a converted value is a guide, never a substitute for a test.
What the calculation is doing
There is no formula that turns one hardness scale into another. Each test loads a different indenter and measures a different thing, so the standard tables are curves drawn through measurements on many steels. The calculator stores the printed values in two tables, hard steel (HRC 20 to 68) and soft steel (HRB 55 to 100), and reads between two rows with a straight line. The fraction of the way up is t = (x − y0) ÷ (y1 − y0), and every other column is z0 + t × (z1 − z0).
Straight lines are used on purpose. The rows are one Rockwell point apart, so a line between them is monotone, cannot overshoot and returns the printed number exactly on a row. A smooth cubic through the same rows differs by at most 0.42 HV, 0.30 HBW and 1.5 MPa, less than the tables round to. Tensile strength in ksi is MPa ÷ 6.894757. For soft steel, where the table has no tensile column, the calculator uses the rule MPa = 3.45 × HBW and labels it as a rule, not a table value.
Why the scales cannot be converted with one formula
Rockwell measures how deep a diamond cone or steel ball sinks under an added load. Brinell divides the load by the curved area left by a 10 mm ball, and Vickers by the area of a small pyramid. They probe different volumes and amounts of strain hardening, so the relationship bends. Going from 20 to 25 HRC adds 27 HBW, but going from 55 to 60 HRC adds 94, so a constant multiplier would be wrong almost everywhere.
Brinell against Vickers shows the pattern. In the soft steel table the two are equal in every row. In the hard steel table Vickers reads 4.5% to 5.7% above Brinell from HRC 20 to 39 and 5.5% to 12.6% above from HRC 40 to 65, where the Brinell ball flattens and the numbers are in brackets. A rule such as "equal below 350 HB" is not what the tables show, so this page does not claim one.
The two tables also meet awkwardly. At 238 HV the hard steel table gives 226 HBW and the soft steel table 238 HBW, a jump of 12 that comes from the standard. Where both apply, the calculator uses the hard steel table, finds the other Rockwell scale through Vickers and prints a note. Alloy, heat treatment and cold work move real steel away from any table, which is why ASTM says to test directly.
Hardness conversion chart for steel, HRC and HRB
Both tables below are generated from the data the calculator reads. Brackets on a Brinell number mean the source prints it in brackets. The tensile column is a table value for HRC 20 to 55 and is not listed above that.
| HRC | HV | HBW | HRA | Tensile MPa | Tensile ksi |
|---|---|---|---|---|---|
| 20 | 238 | 226 | 60.5 | 760 | 110 |
| 25 | 266 | 253 | 62.8 | 840 | 122 |
| 30 | 302 | 286 | 65.3 | 950 | 138 |
| 35 | 345 | 327 | 67.9 | 1,080 | 157 |
| 40 | 392 | 371 | 70.4 | 1,250 | 181 |
| 45 | 446 | 421 | 73.1 | 1,480 | 215 |
| 50 | 513 | 481 | 75.9 | 1,760 | 255 |
| 55 | 595 | 560 | 78.5 | 2,075 | 301 |
| 60 | 697 | (654) | 81.2 | not listed | not listed |
| 65 | 832 | (739) | 83.9 | not listed | not listed |
| 68 | 940 | not listed | 85.6 | not listed | not listed |
For soft steel, HRB 55 to 100, Vickers and Brinell are equal in the source table, Rockwell A appears from HRB 82, and tensile strength is not printed, so the last two columns use the 3.45 × HBW rule of thumb.
| HRB | HV | HBW | HRA | MPa by 3.45 × HBW | ksi by 3.45 × HBW |
|---|---|---|---|---|---|
| 55 | 100 | 100 | not listed | 345 | 50 |
| 60 | 107 | 107 | not listed | 370 | 54 |
| 70 | 125 | 125 | not listed | 430 | 63 |
| 80 | 150 | 150 | not listed | 520 | 75 |
| 90 | 185 | 185 | 55.2 | 640 | 93 |
| 95 | 210 | 210 | 58.3 | 725 | 105 |
| 100 | 240 | 240 | 61.5 | 830 | 120 |
A worked example you can check on paper
Default view, 40 HRC. It is a printed row of the hard steel table: 392 HV, 371 HBW, 70.4 HRA and 1,250 MPa. Tensile strength in ksi is 1,250 ÷ 6.894757 = 181.3.
Between rows, 300 HBW. It lies between HRC 31 (294 HBW, 310 HV, 65.8 HRA, 980 MPa) and HRC 32 (301 HBW, 318 HV, 66.3 HRA, 1,000 MPa). The fraction is t = (300 − 294) ÷ (301 − 294) = 6 ÷ 7 = 0.857. HRC = 31 + 0.857 = 31.86, HV = 310 + 0.857 × 8 = 316.9, HRA = 65.8 + 0.857 × 0.5 = 66.23 and tensile strength = 980 + 0.857 × 20 = 997 MPa, or 144.6 ksi.
Soft steel, 80 HRB. The row reads 150 HV and 150 HBW, with no Rockwell A value because that scale is offered from HRB 82. The table has no tensile column here, so the rule gives 3.45 × 150 = 517.5, shown as 520 MPa or 75 ksi.
Mistakes that catch people out
Converting when you could test. ASTM E140 says conversion is for cases where the material cannot be tested on the specified scale. If a part must meet 30 HRC, measure HRC.
Using the steel table for other metals. Austenitic stainless steel, aluminum, brass and copper have their own tables. Cold worked steel also strays from the table.
Mixing up the Brinell test. The values here are for the 10 mm ball at 3000 kgf. A 500 kgf Brinell reading needs a different table, and a number in brackets, above 58 HRC, is for reference only.
Trusting decimals. The result shows a tenth of an HRC because the interpolation produces it, not because the conversion is that precise. Treat it as a whole number at best.
Reading tensile strength as a guarantee. The tensile figure is a guide. Mill certificates come from tensile tests, and the 3.45 rule runs up to 7.1% off the table across HRC 20 to 55.
Popular calculations
Each opens the calculator with those figures filled in, and they can be changed once it is open. Values in brackets are printed in brackets in the source table.
HRC to HBW and HV
HBW to HRC and HV
HV to HRC and HBW
HRB to HBW and HV
HRA to HRC
Tensile strength to hardness
How this was checked
Every value comes from published copies of ASTM E140, which is paywalled. The hard steel table was read from Thread Check, NBK (citing SAE J417), Miki Pulley and phase2plus, with a zippgroup Vickers table as a fifth check. The soft steel table came from phase2plus, LabTesting and Thread Check. Each of the 144 Vickers, Brinell and Rockwell A cells in the hard steel table matches in at least two sources, and the soft steel Vickers and Brinell columns match in two or more sources for all 46 rows. Three typos in single sources (745 HV for 746, 58.9 HRA for 68.9, 670 HBW for 688) were outvoted. HRC 29 Rockwell A is a two to two tie between 64.8 and 64.7, and 64.8 was kept. Rockwell A at HRB 88 rests on one source to a tenth and another to the whole number. Tensile MPa matches the ksi column of a second source within 1.33% on every row, and a third source within 0.48% at 12 levels.
A script then ran more than 2,400 checks. All seven table columns strictly increase, no scale falls as Vickers rises across 1,681 test points except at the 238 to 226 HBW seam, and 14 round trips such as HRC to HV to HRC return the starting value to better than 1 part in 10 trillion. Examples reproduced: 300 HBW is 31.86 HRC, 316.9 HV and 66.23 HRA from two sources, 60 HRC is 697 HV and 81.2 HRA in three, and 700 HV is 60.13 HRC in three sources against 60.1 in the Vickers keyed table.
The sources all copy the same standard, so this shows the tables were read correctly, not that any steel follows them. The 3.45 rule comes from a University of Washington lecture slide. Pavlina and Van Tyne (2008), who compiled more than 150 non austenitic steels, found that it under predicts tensile strength at higher hardness, and reported a standard error of about 112 MPa for their own hardness to strength fit. Every address listed above was opened and checked at desktop, tablet and phone widths.
Common questions
How do I convert Rockwell C to Brinell?
There is no formula that works for every steel, so it is a table lookup. Read the HRC row in the ASTM E140 table for non austenitic steel: 40 HRC is 371 HBW, 50 HRC is 481 HBW and 55 HRC is 560 HBW. Between rows the calculator draws a straight line between the two nearest rows.
What is the difference between HB, HBS and HBW?
All three are Brinell hardness. HBS was the symbol for a hardened steel ball and HBW is the current one for tungsten carbide, which resists flattening. The published tables print both for the Rockwell C range and the numbers match from HRC 46 downwards. The calculator labels every value HBW.
How accurate are hardness conversions?
They are approximate and the standard says so. ASTM E140 states that conversion should be used only when it is impossible to test the material under the specified conditions, and that values may be inaccurate for a specific application. A guide from a metallography supplier notes that E140 gives no confidence limits, and no source read for this page gives a scatter figure, so this page states no plus or minus.
Can I use it for stainless steel, aluminum or brass?
No. These tables are for non austenitic steels: carbon, low alloy and tool steel. ASTM E140 prints separate tables for austenitic stainless steel, nickel alloys, brass, copper and wrought aluminum, and they give different answers for the same Rockwell number. The calculator does not include them.
What tensile strength does a Brinell number give for steel?
A common rule of thumb for steels is tensile strength in MPa about 3.45 times the Brinell number, or 500 times in psi. For 300 HBW that is 1,035 MPa, while the E140 table reads 997 MPa, so the rule is 3.8% high. Across HRC 20 to 55 the table divided by Brinell runs from 3.30 to 3.71, so the rule can be about 7% off.
Why does the calculator refuse some values?
Each scale is only valid over the range the table covers: Rockwell C 20 to 68, Rockwell B 55 to 100, Brinell 100 to 739 and Vickers 100 to 940. Outside that there is no row to read and extrapolating would be a guess. The message says which limit you passed and which scale to try, such as Rockwell B for steel softer than 20 HRC.
Related Calculators and Reference
- Mohs Hardness Identification Tool: the scratch scale for minerals, a different measure from indentation hardness.
- Modulus of Elasticity of Steel: stiffness, which is nearly the same across steel grades however hard they are.
- A36 Steel Yield Strength: a common structural steel to set beside a strength estimate from hardness.
- Unit Weight of Steel: the weight of the steel once its hardness and grade are settled.
- Pressure Converter: convert stress figures between psi and the metric pressure units.
- ASTM E140 standard hardness conversion tables for metals: the standard behind these tables, with its scope and its rule that conversion is for cases where direct testing is impossible.