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Hardness Conversion: HRC, HB, HV and Tensile

Guide · Updated October 28, 2026

Hardness is measured on several scales, and a drawing, a heat treat cert and your tester often use different ones. ASTM E140 gives conversion tables between Rockwell, Brinell, Vickers and other scales for steel and some other metals. The conversions are empirical, so they are approximate, and they only apply to the material group the table was made for. When a spec calls for a scale, test on that scale if you can.

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Step by step

Note the scale and material: HRC, HRB, HB or HV, and whether the part is carbon or alloy steel.
Use the right table: ASTM E140 has separate tables for steels, nickel alloys, brass and others.
Interpolate: Read between rows for values not listed.
Estimate tensile if needed: For steel, tensile strength in psi is roughly 500 × HB.
Report both: Write the measured value and scale and note that the other is converted.

Approximate conversions for steel

HRC 20 ≈ 238 HV ≈ 226 HB ≈ 110 ksi tensile
HRC 25 ≈ 266 HV ≈ 253 HB
HRC 30 ≈ 302 HV ≈ 286 HB ≈ 138 ksi
HRC 35 ≈ 345 HV ≈ 327 HB
HRC 40 ≈ 392 HV ≈ 371 HB ≈ 181 ksi
HRC 45 ≈ 446 HV ≈ 421 HB
HRC 50 ≈ 513 HV ≈ 481 HB
HRC 55 ≈ 595 HV
HRC 60 ≈ 697 HV
HRC 65 ≈ 832 HV

Values are rounded from the ASTM E140 steel table. Above about 450 HB a carbide ball must be used for Brinell, and many tables stop listing Brinell. Tensile values above about 50 HRC are not reliable estimates.

Rockwell B range

Softer steels are tested on Rockwell B. Approximate values: HRB 70 ≈ 125 HB, HRB 80 ≈ 150 HB, HRB 90 ≈ 185 HB, HRB 100 ≈ 240 HB. Below about HRC 20, use HRB; HRC readings under 20 are not considered accurate.

Estimating tensile strength

For carbon and low alloy steels, ultimate tensile strength is roughly 500 × HB in psi, or about 3.45 × HB in MPa. For 286 HB this gives 143 ksi (986 MPa), close to the 138 ksi in the E140 table. It is only an estimate and is not valid for stainless, cast iron or nonferrous metals.

Worked example: prehard 4140

A bar sold as 4140 prehard reads 30 HRC. That converts to about 286 HB and about 140 ksi tensile. A drawing that calls 28 to 32 HRC is met. If a customer asks for 269 to 321 HB, 30 HRC is inside that too, but note on the report that the HB value is converted from HRC.

Worked example: heat treat check

An O1 punch reads 59 HRC after tempering. That is roughly 675 HV. A spec of 650 HV minimum is met by conversion, but since the two scales use different indenters and loads, a dispute would be settled by a Vickers test on the part.

Common problems

Converting between scales for the wrong material, testing on a curved surface without the correction, testing too close to an edge or on decarburized skin, and testing thin parts where the anvil shows through. Verify the tester each day on a certified test block.

FAQ

What is 30 HRC in Brinell?

About 286 HB for steel per ASTM E140.

Can I convert HRC to tensile strength?

Roughly, for steel: about 500 × HB in psi. 30 HRC is about 138 ksi.

Are conversions exact?

No. They are empirical and approximate, and depend on the material.

How do I check part size after heat treat?

Check the gage itself before trusting a measurement: gage blocks set mics, calipers and indicators; build any stack free at gageblockcalc.com.

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General shop information only — follow your drawing, tool maker's data and your quality system.