Hardness Conversion Calculator: Rockwell C, Rockwell B, Vickers, Brinell and Tensile Strength
Convert steel hardness between Rockwell C, Rockwell B, Vickers, Brinell and Rockwell A, with interpolation and approximate tensile strength.
How it works
No exact formula links the scales; values come from the steel conversion table (ASTM E140 Table 1 basis). Between two rows: t = (x − x₁) ÷ (x₂ − x₁), y = y₁ + t × (y₂ − y₁). Tensile strength (approx.) ≈ 3.2–3.5 × HB in MPa.
Hardness tests press an indenter into the metal in different ways: Rockwell measures the depth of a diamond cone (C and A scales) or a steel or carbide ball (B scale), while Vickers and Brinell measure the size of a diamond-pyramid or ball impression. Because each test deforms the metal differently, no single formula converts between them. Standards bodies built empirical tables by testing the same steels on every scale, and ASTM E140 Table 1 is the reference for non-austenitic steels. The calculator converts your value to Vickers using the table, then reads every other scale at that Vickers value, interpolating linearly between neighbouring rows instead of rounding to the nearest row. It also shows the nearby table rows so you can check. Each scale has a valid range: Rockwell C from about 20 to 68 HRC, Rockwell B up to 100 HRB, and Brinell with a carbide ball up to about 650 HBW. Values outside these ranges are flagged as reference only. The tensile strength column is an approximate correlation, useful for screening steel but not for design. The table is for steel; other metals such as aluminum, brass or stainless steel have their own tables. This page is about metal hardness; water hardness (calcium and magnesium in water) is a different topic with its own calculator.
Worked example
A heat-treated part tests at 40 HRC. 40 HRC is a row of the steel table: 392 HV, 371 HBW, 70.4 HRA and an approximate tensile strength of 1,250 MPa (181 ksi). Rockwell B does not apply at this hardness (it is above the HRB range). A reading between rows, such as 40.5 HRC, is interpolated: halfway between 392 and 402 HV gives 397 HV.
Sources: NBK: Conversion table of hardness (based on ASTM E140 Table 1) · Tubing China: Hardness conversion chart (HB, HV, HRB, HRC, UTS) · Omni Calculator: Hardness conversion
Frequently asked questions
How do I convert HRC to Brinell?
Use the steel conversion table: for example 30 HRC ≈ 286 HBW, 40 HRC ≈ 371 HBW and 50 HRC ≈ 481 HBW. Choose Rockwell C as the input and Brinell as the main result to interpolate any value in between.
What is 60 HRC in Vickers?
About 697 HV on the steel table. Knife steels at 58–62 HRC correspond to roughly 653–746 HV.
Can you convert hardness to tensile strength?
Roughly, for carbon and alloy steels: tensile strength in MPa is about 3.2 to 3.5 times the Brinell number. 40 HRC (371 HBW) corresponds to about 1,250 MPa. The correlation is approximate and does not hold for other metals or for cold-worked material.
Why does HRC stop at 20 and HRB at 100?
Below about 20 HRC the diamond cone sinks too deep to give reliable readings, so softer steels are tested with the B-scale ball. Above 100 HRB the ball test becomes insensitive and may flatten the ball, so harder steels are tested on the C scale.
Are hardness conversions exact?
No. They are empirical averages for steel, and each conversion adds uncertainty. Standards say converted values should be reported as approximate, for example "40 HRC (converted from 392 HV)".
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Hardness conversions are approximate. Do not use converted values or estimated tensile strength for safety-critical design or acceptance testing.