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Hardness to Tensile Strength Estimate Calculator (Brinell HB to MPa and ksi)

Hardness testing is quick and cheap, a tensile test is not. This calculator turns a Brinell reading into a rough ultimate and yield strength for steel so you can screen material and decide whether a formal tensile test is needed.

Your numbers

HB

Brinell hardness (HBW 10/3000) of the part, ideally the mean of several readings.

The common rule UTS (MPa) is about 3.45 x HB applies to carbon and low-alloy steels. It does not apply to austenitic stainless, aluminum or cast iron.

0.7 ratio

Typical 0.6 to 0.75 for normalized steel and 0.8 to 0.9 for quenched and tempered grades.

MPa

Specification minimum from the drawing or material standard.

Your results

Estimated ultimate tensile strength
690
Rule-of-thumb estimate in MPa.
Margin over required UTS
15%
Negative means the estimate falls below the requirement.
Estimated UTS (ksi)
100.076
Estimated yield strength
483
UTS multiplied by the yield ratio you chose.
Estimated yield strength (ksi)
70.0532

Hardness-based strength is an approximation for screening only. It is not a substitute for a tensile test where the specification demands one.

Save results:

Estimated UTS and yield (MPa) vs Brinell hardness

Sweeps Brinell hardness from 120 to 450, holding your other inputs fixed.

Inspection plans from your ERP data

Want hardness limits and lot results tracked in your ERP inspection plans? Ask for an optional expert review.

Optional. The tool and every export work without this. No spam.

How to use it

Enter the Brinell hardness, choose a conversion factor and a yield ratio, then compare against the minimum strength on the drawing. The margin output shows how far above or below the requirement the estimate sits. The chart sweeps hardness so you can see the hardness window that would satisfy a strength requirement, which is handy when you set an incoming inspection acceptance range.

  • Average at least three indentations
  • Test on a prepared, decarb-free surface
  • Use the factor that matches your steel family
  • Treat a thin margin as a reason to run a tensile test

The rule behind the estimate

For carbon and low-alloy steels, ultimate tensile strength in MPa is close to 3.45 times the Brinell number. ASTM A370 gives conversion tables and notes the limits of such conversions. The relation works because both hardness and tensile strength reflect resistance to plastic deformation, but work hardening differs by alloy. Austenitic stainless steels, aluminum alloys, copper alloys and cast irons follow different relations, so this factor should not be reused for them.

Worked example

A forged shaft reads 235 HB. With the typical factor of 3.45, the estimated UTS is about 811 MPa, or roughly 118 ksi. With a yield ratio of 0.7 the estimated yield is about 568 MPa. Against a drawing minimum of 600 MPa the margin is about 35 percent, so the part is comfortably inside. A reading of 170 HB would give 587 MPa, below the requirement, and should be held for tensile testing or rejected per procedure.

Common mistakes and ERP notes

Common errors are applying the steel factor to stainless or aluminum, testing a case-hardened surface and inferring core strength, and ignoring heat-to-heat variation. In ERP, store the hardness range as an inspection characteristic on the incoming or in-process plan so each lot records actual readings against the limits. Linking those results to the batch or heat number makes later traceability and certificate of conformance checks much simpler.

  • Record the test scale and load with the reading
  • Tie results to the heat or lot number
  • Keep the tensile test requirement separate from hardness screening

Frequently Asked Questions

Is UTS really 3.45 times Brinell?

It is a long-standing rule of thumb for carbon and low-alloy steels, with scatter of roughly plus or minus 10 percent. It should be used for screening. For acceptance against a specification, run a tensile test as the standard requires.

Can I use this for stainless steel or aluminum?

No. Austenitic stainless work hardens strongly and aluminum alloys follow different relations, so the steel factor gives misleading values. Use material-specific conversion tables or tensile testing for those families.

How do I convert between MPa and ksi?

Divide MPa by 6.894757 to get ksi, or multiply ksi by 6.894757 to get MPa. The calculator shows both so you can compare with metric and US specifications without a separate conversion step.

What yield ratio should I use?

Normalized and annealed steels commonly sit between 0.6 and 0.75, while quenched and tempered steels reach 0.8 to 0.9. If you know the grade, use its typical value, or use a measured value from past certificates.

If incoming hardness readings sit in spreadsheets, we can help route them into inspection plans and lot records in your ERP.

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