Hardness Conversion Calculator Formula

Understand the math behind the hardness conversion calculator. Each variable explained with a worked example.

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Formulas Used

Approx. UTS (steel)

uts_mpa = 3.45 * hb

Approx. UTS

uts_ksi = 3.45 * hb * 0.145038

Approx. Rockwell B (HRB)

hrb_approx = (hb - 49) / 2.8 + 35

Variables

VariableDescriptionDefault
hbBrinell Hardness (HB)200

How It Works

Hardness to Strength Conversion

For carbon and alloy steels, Brinell hardness (HB) correlates approximately with ultimate tensile strength.

Empirical Relationship

UTS (MPa) ≈ 3.45 × HB

This approximation is valid for steels in the range HB 120-450. For non-ferrous metals or very high-strength steels, the conversion factor differs. The Rockwell B approximation is a rough linear mapping useful for quick estimates.

Worked Example

A steel part has a measured Brinell hardness of 200 HB.

hb = 200
  1. 01UTS ≈ 3.45 × 200 = 690 MPa
  2. 02In ksi: 690 × 0.145 = 100.1 ksi
  3. 03Approx. HRB = (200 - 49) / 2.8 + 35 = 53.9 + 35 = 88.9

Frequently Asked Questions

How accurate is the HB to UTS conversion?

For carbon and alloy steels in the HB 120-450 range, the approximation is within about 10%. Outside this range or for other materials, the accuracy decreases significantly.

What is the difference between Brinell and Rockwell hardness?

Brinell uses a steel or carbide ball with a known load and measures indentation diameter. Rockwell measures indentation depth with various indenters (B scale uses a ball, C scale uses a diamond cone).

Can hardness testing replace tensile testing?

For approximate screening or quality control, yes. Hardness is quick, non-destructive (practically), and correlates with strength. For formal material certification, a tensile test is still required.

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