Hardness Conversion Calculator
Rockwell, Vickers, Brinell and Knoop equivalents for steel, from ASTM E140 or ISO 18265.
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- Free preview: the names of the scales in the table’s first rows (up to 3), with the equivalent you convert to, the working and every other value hidden.
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Results are estimates from the formulas shown, not a professional design or certification. Have a qualified engineer verify anything safety-critical (structures, electrical installations, gas or pressure systems).
About the Hardness Conversion Calculator
Convert a hardness reading between Rockwell C, B, A, D and F, the superficial Rockwell scales (15N, 30N, 45N, 15T, 30T, 45T), Vickers (HV), Brinell (HBW) and Knoop (HK), and estimate the tensile strength of steel. Choose the table: ASTM E140 for non-austenitic carbon, alloy and tool steels (Table 1 in the Rockwell C range, Table 2 in the Rockwell B range) or ISO 18265 Table A.1 for unalloyed and low-alloy steels and cast steel. Values between the printed rows are interpolated linearly, and the calculator tells you when a value is outside a scale’s range or only an approximation.
Two more calculations work from the indentation itself: Brinell hardness from the measured diameter (with the d/D, force-ratio and thickness checks of ISO 6506-1) and Vickers hardness from the two diagonals (ISO 6507-1), each with its equivalents on the other scales. Conversions are approximate by nature — for acceptance against a specification, test on the scale it names.
Without a pass, the free preview works on your own reading and shows the names of the scales in the table’s first rows and the notes that apply, with the equivalent you convert to, the working and every other value hidden; the full result, Copy result and the CSV come with a Pro pass.
How to use it
- Choose Convert a value, the scale your reading is on and the value — for example 40 HRC or 450 HV. For a tensile strength, choose the ISO 18265 table and Rm.
- Pick the conversion table: ASTM E140 for non-austenitic steels, or ISO 18265 Table A.1 for unalloyed and low-alloy steels and cast steel. Show first puts the scale you need at the top.
- Read the equivalents. A dash means the hardness is outside that scale’s range (Rockwell C below about 20, Rockwell B above 100); values marked as approximations are printed in brackets in the standard.
- To work from a test, choose Brinell from the indentation (ball, force and the measured diameter, or two diameters at right angles) or Vickers from the diagonals (force and both diagonals).
- Copy the result or download every scale as a CSV — with a Pro pass, or after unlocking this result.
Examples
ASTM E140, Rockwell C 40
392 HV, 371 HBW, 402 HK, 70.4 HRA, 55.4 HRD, 80.4 HR15N, 59.5 HR30N, 43.1 HR45N; tensile strength about 1,262 MPa (183 ksi) by ISO 18265
ASTM E140, Vickers 450
45.3 HRC — 450 HV lies a third of the way from 446 HV (45 HRC) to 458 HV (46 HRC)
ASTM E140 Table 2, Rockwell B 90
185 HV, 185 HB, 201 HK, 55.2 HRA, 89.9 HR15T, 76.4 HR30T, 62.8 HR45T
ISO 18265 Table A.1, Rm 800 MPa
250 HV, 238 HB, 99.5 HRB, 115.1 HRF, 22.2 HRC
HBW = 0.102 × 2 × 29,420 N ÷ (π × 10 × (10 − √(100 − 16)))
229 HBW 10/3000; d/D = 0.40, depth 0.417 mm, so the part must be at least 3.34 mm thick
HV = 0.1891 × 98.07 N ÷ (0.202 mm)²
455 HV 10, about 45.7 HRC by ASTM E140
Common uses
- Reading a supplier certificate in HB or HV against a drawing that specifies HRC (or the other way round)
- Estimating the tensile strength of a steel part you can only hardness-test
- Choosing a superficial Rockwell scale for thin material or a case, and knowing its HRC equivalent
- Working out HBW and HV from microscope readings of the indentation, with the validity checks
How the conversion works
Each table lists equivalent hardness numbers row by row. Your value is first placed on the table’s key scale — Vickers in ISO 18265 Table A.1, Rockwell C in ASTM E140 Table 1, Rockwell B in Table 2 — by linear interpolation between the two neighbouring printed values of its own column, and every other scale is then read the same way. The working shows both steps. A scale that the table does not cover at that hardness gets no value rather than an extrapolated guess.
The formulas of the indentation tests
- Brinell (ISO 6506-1, ASTM E10): HBW = 0.102 × 2F ÷ (πD(D − √(D² − d²))), F in newtons, D the ball and d the indentation diameter in mm. Valid for 0.24D ≤ d ≤ 0.6D and up to 650 HBW; the test piece must be at least 8 times as thick as the indentation is deep, h = (D − √(D² − d²))/2. The force-diameter ratio 0.102·F/D² is 30 for steel.
- Vickers (ISO 6507-1, ASTM E92): HV = 0.102 × 2F·sin(136°/2) ÷ d² = 0.1891 F/d², with d the mean of the two diagonals in mm. The indentation is about d/7 deep and the test piece must be at least 1.5d thick. ISO 6507-1 names three force ranges: the Vickers test (49.03 N and over), the low-force test (1.961 N to under 49.03 N) and the microhardness test (0.09807 N to under 1.961 N).
What the tables cover
ASTM E140 Tables 1 and 2 are for non-austenitic carbon, alloy and tool steels in the as-forged, annealed, normalised and quenched-and-tempered conditions, provided they are homogeneous (ASTM E140); the standard has other tables for nickel alloys, brass, copper, austenitic stainless steel, white cast iron and aluminium, which this calculator does not include. ISO 18265 Table A.1 is for unalloyed and low-alloy steels and cast steel; the standard gives further tables for other groups of materials. The two tables were drawn up from different test data, so they differ by a few tenths of a Rockwell point and a few Vickers points.
Limitations
- Only the steels each table names: not austenitic stainless steels, cast iron, cold-worked or case-hardened parts, or non-ferrous metals.
- Conversions are approximate. ASTM E140 says they should be used only when testing under the specified conditions is impossible; a specification limit should be tested on its own scale.
- Tensile strength from hardness is an estimate for steels: scatter of ±10 % or more is normal, and it is no substitute for a tensile test.
- The equivalents after a Brinell test are given for the 10 mm ball with 3000 kgf (ratio 30), the condition the tables use.
- An estimate for checking and learning — not a professional design or a test certificate.
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Frequently asked questions
What do I get without a pass?
Without a pass, Hardness Conversion Calculator shows the names of the scales in the table’s first rows (up to 3), with the equivalent you convert to, the working and every other value hidden. Until you unlock it, the result can’t be downloaded or copied. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
How do I convert HRC to HV?
Read it from a conversion table for your material. For non-austenitic steels ASTM E140 Table 1 gives, for example, 40 HRC ≈ 392 HV, 50 HRC ≈ 513 HV and 60 HRC ≈ 697 HV; between rows, interpolate linearly. ISO 18265 Table A.1 gives almost the same values for unalloyed and low-alloy steels.
Can hardness be converted to tensile strength?
Approximately, for steel. ISO 18265 Table A.1 lists the tensile strength Rm beside the hardness for unalloyed and low-alloy steels and cast steel: 250 HV ≈ 800 MPa and 400 HV ≈ 1,290 MPa. Expect a scatter of 10 % or more; a tensile test gives the real value.
Why do ASTM E140 and ISO 18265 give slightly different numbers?
They were compiled from different sets of comparison tests. In the Rockwell C range they agree within a few tenths of a point; in the soft range they differ more — ISO puts 240 HV at 98.1 HRB, ASTM puts it at 100 HRB. Use the table your specification refers to.
What is the difference between HB and HBW?
HBW is Brinell hardness measured with a tungsten-carbide ball, the only ball current ISO 6506-1 and ASTM E10 allow; the older HBS used a steel ball. Below about 450 they give practically the same number, but steel balls flatten on harder material. The test covers hardness up to 650 HBW.
How do I calculate Brinell hardness from the indentation?
HBW = 0.102 × 2F ÷ (πD(D − √(D² − d²))), with F in newtons and the ball diameter D and indentation diameter d in millimetres. A 10 mm ball under 3000 kgf (29.42 kN) leaving a 4.00 mm indentation gives 229 HBW. The indentation must measure between 0.24 and 0.6 of the ball diameter.
Does this work for stainless steel or aluminium?
No. Austenitic stainless steels, aluminium, copper alloys and cast iron work-harden and recover differently, so they have their own conversion tables (ASTM E140 lists several). Using the steel tables for them can be wrong by a lot.