Hardness Conversion Calculator: Scales & Chart

This hardness conversion calculator converts between common hardness scales: Brinell (HB), Rockwell B (HRB), Rockwell C (HRC), Vickers (HV), and Shore D. Enter a hardness value on any one scale, and the calculator returns the equivalent values on the other scales, plus an approximate tensile strength (MPa) for steels. The conversion uses the standard ASTM E140 tables, which are valid for carbon steels, alloy steels, and tool steels.

Formula

The conversion between hardness scales is not a single simple equation; it is based on empirical tables (ASTM E140) that map equivalent hardness values. The calculator uses linear approximations of those tables for the common range. The main relationships are:

• HB to HRC: HRC ≈ (HB + 100) / 7.5 (valid roughly for HB 150–450)
• HRC to HB: HB ≈ (HRC × 7.5) − 100
• HB to HV: HV ≈ 1.05 × HB (approximate, varies slightly by alloy)
• HB to tensile strength (steel): TS (MPa) ≈ 3.45 × HB

Where HB is Brinell hardness, HRC is Rockwell C, HV is Vickers, and TS is ultimate tensile strength. All values are dimensionless hardness numbers except TS, which is in megapascals (MPa).

Worked Example

Suppose you have a steel with a Brinell hardness of 200 HB. Using the calculator defaults:

1. Convert HB to HRC: (200 + 100) / 7.5 = 40.0 HRC
2. Convert HB to HV: 200 × 1.05 = 210 HV
3. Estimate tensile strength: 200 × 3.45 = 690 MPa

The calculator returns 40.0 HRC, 210 HV, and 690 MPa for an input of 200 HB. This matches the ASTM E140 table within a few points.

Why Hardness Conversion Matters

Hardness tests are quick and non-destructive, making them ideal for quality control. But different industries and regions favor different scales. A fastener manufacturer might use Rockwell C, while a European supplier might quote Vickers. Conversion lets you compare specs without re-testing. It also gives a rough tensile strength estimate, which is useful for material selection and failure analysis. However, conversions are only valid within the calibrated range of each scale and for similar material types (e.g., steel-to-steel).

How to Choose the Right Input Scale

You can enter any one of the three scales; the calculator will convert to the others. Choose the scale that matches your existing data. For example:

• If you have a Rockwell C value (common in heat treating), enter it in the HRC field.
• If you have a Brinell value (often used for softer steels and castings), enter HB.
• If you have a Vickers value (common in thin sections and case-hardened parts), enter HV.

Leave the other inputs at 0. The calculator will compute the remaining scales. Note that the linear approximations are most accurate in the mid-range: HB 150–450, HRC 20–50, HV 150–500. Outside that range, errors can exceed 5%.

Common Mistakes and Pitfalls

One frequent error is mixing up Rockwell B and Rockwell C scales. Rockwell B (HRB) is for softer materials (aluminum, brass) and uses a 1/16-inch ball indenter; Rockwell C (HRC) is for hardened steel and uses a diamond cone. The conversion formulas are completely different. Another mistake is ignoring the load or indenter type within a scale—e.g., Vickers HV30 vs HV5. The calculator assumes standard loads. Also, conversions are not valid for non-ferrous metals or ceramics; the ASTM E140 tables are specifically for steel. Always state the scale and load when quoting a hardness value.

Limitations of the Formula

The linear approximations are derived from the ASTM E140 standard, which itself is a table of empirical data. The table is not perfectly linear, so the formulas deviate slightly at the extremes. For example, at HB 600, the formula gives HRC = 93.3, but the actual table value is about 60 HRC. The linear relationship breaks down above HB 450. For high-hardness values (HRC > 50), use a more precise polynomial or the full table. Also, the tensile strength correlation (TS ≈ 3.45 × HB) is a rough rule of thumb; actual values vary with alloy composition and heat treatment. Use it only for preliminary estimates.

Frequently Asked Questions

What is the difference between Rockwell B and Rockwell C?

Rockwell B (HRB) uses a 1/16-inch steel ball indenter with a 100 kg load, suitable for soft materials like annealed steel, aluminum, and brass. Rockwell C (HRC) uses a diamond cone with a 150 kg load, for hardened steel and hard alloys. The scales overlap in the range of about HRB 70–100, but they are not interchangeable.

Can I convert hardness to tensile strength exactly?

No. The relationship between hardness and tensile strength is empirical and approximate. For steels, a common rule is TS (MPa) ≈ 3.45 × HB, but the constant varies from 3.2 to 3.8 depending on the alloy and heat treatment. The conversion is useful for quick estimates but not for final design.

Why does my hardness value not match the conversion table?

Because hardness tests are affected by surface preparation, load, indenter type, and material thickness. Also, the conversion tables are averages; individual materials can deviate by several points. Always ensure you are using the correct scale and test method.

Which hardness scale is the most accurate?

No single scale is universally accurate. Vickers and Knoop are the most precise for small parts and thin sections, while Brinell is best for coarse-grained materials. Rockwell is fast and widely used in industry. Accuracy depends on the material and the operator.

Can I use this calculator for aluminum or other non-ferrous metals?

No. The conversion formulas are based on steel data. Non-ferrous metals like aluminum, copper, and titanium have different hardness-to-strength relationships. Use specific conversion tables for those materials.

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in hb | Brinell (HB) | HB | 200 | 0
in hrc | Rockwell C (HRC) | HRC | 0 | 0
in hv | Vickers (HV) | HV | 0 | 0
out hrc_out | Rockwell C (HRC) | HRC | (hb+100)/7.5 | 1
out hb_out | Brinell (HB) | HB | (hrc*7.5)-100 | 0
out hv_out | Vickers (HV) | HV | hb*1.05 | 0
out ts | Tensile strength (MPa) | MPa | hb*3.45 | 0