Alloy Hardness Converter

Introduction to hardness scale conversion

Hardness numbers show how strongly a material resists indentation, but the number is always tied to the test method that produced it. That is why a report that lists 250 BHN, another that lists 237 HV, and a heat-treatment note that says 19 HRC may all be describing roughly similar material conditions without using the same scale. This calculator gives you a quick way to translate between Brinell (BHN), Vickers (HV), Rockwell B (HRB), and Rockwell C (HRC) so you can compare drawings, supplier certificates, lab notes, and classroom examples more easily.

The most important idea to keep in mind is that a hardness conversion is an engineering estimate, not a law of nature. Brinell, Vickers, and Rockwell tests do not use the same indenter shape, load, or penetration depth, so there is no universal exact equation that makes every scale interchangeable for every alloy. In practice, engineers still convert between scales all the time because approximate relationships are extremely useful for screening materials, checking whether a batch looks plausible, and translating one specification into the language used by another team.

This page is meant to help with that practical job. The explanation below walks through what each input means, how the formulas are organized, where the assumptions matter, and how to judge whether a converted value passes a basic sanity check. If you are doing compliance work, a final inspection sign-off, or any safety-critical decision, use this tool as a first pass and then confirm with recognized ASTM or ISO tables and direct testing on the actual material.

How the hardness converter works

The calculator accepts one measured hardness value and asks two simple questions: what scale was the value reported in, and what scale do you want to see it in? Once you answer those, it estimates an equivalent value in the target scale using lightweight empirical relationships that are easy to evaluate in a browser. That makes the tool fast enough for quick checks while still being transparent about the underlying math.

Internally, the tool uses Brinell hardness as a bridge scale. If you enter a Vickers, HRB, or HRC number, the script first estimates the corresponding BHN value. It then converts that internal BHN estimate to your requested output scale. This two-step structure keeps the calculator consistent from one conversion path to another and mirrors the way many printed shop references organize their tables.

How to use the converter

1. Enter the measured hardness in Value. For example, enter 250 if a report says 250 BHN, or 60 if it says 60 HRC.
2. Select the scale the value is currently reported in under From Scale.
3. Select the desired output scale under To Scale.
4. Select Convert. The result appears in the results panel and can be copied with Copy Result.

If you are checking several materials in a row, it helps to keep the original source scale written down beside each value. The most common shop-floor mistake is not the arithmetic; it is accidentally treating an HRB number as HRC, or vice versa. Recording the source scale prevents that mix-up and makes later reviews much easier.

Common hardness scales and what the symbols mean

Hardness values are dimensionless numbers derived from indentation tests. The result is meaningful only when you know the test method behind it. The four scales in this calculator cover many everyday engineering situations in metals work, especially steels and related alloys.

• BHN (Brinell) uses a ball indenter and is often applied to castings, forgings, and general steel checks where a larger indentation is acceptable. It is useful when surfaces are not perfectly polished and when you want a broad indication of bulk hardness.
• HV (Vickers) uses a diamond pyramid and is common in laboratories, metallography, and microhardness work. Because Vickers can be used at many loads, it is flexible for both bulk materials and thinner sections.
• HRB (Rockwell B) is typically used for softer metals, mild steels, and some non-ferrous alloys. It is common where the Rockwell C scale would be too severe or too low in sensitivity.
• HRC (Rockwell C) uses a diamond cone and is widely used for hardened steels, tool steels, and case-hardened parts. It is one of the most familiar heat-treatment specification scales.

These tests all answer a similar question, but they do not probe the material in exactly the same way. That is why the relationship between scales depends on the material family, microstructure, surface condition, and hardness range. A conversion that is reasonable for a low-alloy steel may be less reliable for a cast iron, a heavily cold-worked stainless steel, a thin coating, or a part with a steep hardness gradient from surface to core.

Model and formulas used

The calculator uses simplified linear relationships that are convenient for quick engineering estimates. They are best treated as rule-of-thumb conversions, especially for many carbon and low-alloy steels in common working ranges. The tool is intentionally transparent: you can reproduce every result with the formulas listed below.

Conversions to BHN as the internal step:

• From BHN: BHN = BHN
• From HV: BHN ≈ 0.95 × HV
• From HRB: BHN ≈ 4.7 × HRB + 20
• From HRC: BHN ≈ 9.5 × HRC + 70

Conversions from BHN to the requested output:

• To HV: HV ≈ BHN / 0.95
• To HRB: HRB ≈ (BHN − 20) / 4.7
• To HRC: HRC ≈ (BHN − 70) / 9.5

The Brinell–Vickers relationship deserves a note, because it is easy to get backwards: for steels in common ranges, the Vickers number runs about 5 percent higher than the Brinell number for the same material (200 HB ≈ 210 HV in the ASTM E140 correlations), which is why the tool divides by 0.95 on the way out to HV rather than multiplying.

Sources: the authoritative correlations are the piecewise, material-specific tables in ASTM E140, Standard Hardness Conversion Tables for Metals (and ISO 18265). The linear fits used here track those tables loosely for non-austenitic steels — expect deviations of roughly 10–20 percent in mid-range Rockwell C conversions and more outside steel — and the HB ≈ 0.95 × HV relationship is the standard steel approximation. Last reviewed July 2026.

A useful way to read these equations is to see BHN as the shared middle language of the calculator. That does not mean Brinell is somehow more fundamental than the other scales in all materials; it simply means the page uses BHN as a stable internal reference so that every conversion path is handled consistently.

Example formula (MathML)

One of the relationships used is the approximate conversion from Brinell to Rockwell C:

Worked examples across the four scales

Worked examples are useful because they let you confirm not only the arithmetic but also your intuition. If the converted number lands far outside the range you expected for the material condition, that is a clue to re-check the source scale, the heat-treatment state, or the applicability of the estimate.

Example 1: Convert 250 BHN to HV, HRB, and HRC

Suppose a supplier datasheet lists a steel at 250 BHN. You want to compare that against a specification written in Vickers or Rockwell terms.

1. To HV: HV ≈ 250 / 0.95 ≈ 263.2 HV.
2. To HRB: HRB ≈ (250 − 20) / 4.7 ≈ 230 / 4.7 ≈ 48.9 HRB.
3. To HRC: HRC ≈ (250 − 70) / 9.5 ≈ 180 / 9.5 ≈ 18.9 HRC.

The practical interpretation is that this is not extremely hard steel. A value around 19 HRC is compatible with many medium-strength conditions, but it would be far below what you expect from a hardened cutting tool or a heavily case-hardened wear surface.

Example 2: Convert 60 HRC to BHN and HV

Now consider a hard tool steel measured at 60 HRC. The calculator first estimates BHN, then converts to any requested output scale.

1. HRC to BHN: BHN ≈ 9.5 × 60 + 70 = 570 + 70 = 640 BHN.
2. BHN to HV: HV ≈ 640 / 0.95 ≈ 673.7 HV.

That result sits in a much harder region than the previous example, which matches expectations for wear-resistant steels. If a high HRC input ever converts to a surprisingly low BHN or HV value, the first thing to check is whether the wrong Rockwell scale was selected.

Example 3: Common mistake check with HRB versus HRC

Rockwell B and Rockwell C are easy to confuse because both are often abbreviated as Rockwell hardness in conversation. However, they serve different hardness ranges. As a quick plausibility check, 90 HRB can be reasonable for mild steel, while 90 HRC is generally unrealistic for steel. If you accidentally treat 90 as HRC, the internal estimate becomes BHN ≈ 9.5 × 90 + 70 = 925, which should immediately look suspicious.

Sanity checks and typical ranges

These broad bands are not acceptance limits, but they are helpful for spotting obvious data-entry errors. Think of them as a quick gut-check for steels and similar engineering alloys.

• BHN: about 120 to 220 for many mild or structural steels, about 250 to 350 for stronger steels, and up into the 600 range for very hard surfaces or tool steels.
• HV: about 130 to 700 is common across many engineering steels, with higher values possible in special cases and coating work.
• HRB: roughly 40 to 100 for softer metals and mild steels.
• HRC: roughly 20 to 40 for many quenched-and-tempered steels, and about 50 to 65 for harder tool steels or case-hardened surfaces.

Another good sanity check is context. A drawing that calls for wear resistance, edge retention, or a hardened case should not usually convert into a very low hardness band. On the other hand, a ductile formed part or low-carbon sheet product should not suddenly appear in a high-HRC region unless there is a special treatment involved.

Reference table

The table below uses the same formulas as the calculator, so the values are internally consistent with the page results. Published standards may differ because many official tables are non-linear and material specific.

Limitations, assumptions, and best practices

This converter is intentionally simple so it stays fast and readable. That simplicity is a strength for quick estimates, but it also means you should understand where the result becomes less trustworthy.

Assumptions behind the numbers

• Material dependence: The linear relationships are most reasonable for many carbon and low-alloy steels. Error can grow for cast irons, precipitation-hardened alloys, austenitic stainless steels, aluminum alloys, copper alloys, powdered metals, and other special cases.
• Range dependence: Mid-range values are usually the most comfortable territory for simple fits. Very soft or very hard extremes can depart more strongly from straight-line estimates.
• Surface versus bulk response: A case-hardened part can have a hard shell and a softer core. Different hardness methods sample different depths, so a single converted value cannot fully represent a through-thickness gradient.
• Test variability: Surface preparation, calibration, indenter wear, dwell time, operator technique, and local microstructure all affect the original reading. Converting an uncertain measurement into another scale does not remove that uncertainty.
• Rounding: This page displays the final result to one decimal place. Small differences versus other references are normal.

Best practices for interpreting the result

• Confirm the reported scale before converting. HRB and HRC are the most common source of confusion.
• Use the conversion as a comparison tool. It is excellent for translating specifications, screening batches, and building intuition, but it does not replace a required direct test method.
• Cross-check with context. If you also know tensile strength, treatment condition, or expected wear behavior, make sure the converted hardness is in the same general neighborhood.
• Be conservative for critical design choices. Treat the converted number as approximate and allow for uncertainty rather than using it as an exact threshold.
• Prefer official standards for regulated work. When certification, compliance, or safety-critical acceptance is involved, use recognized conversion tables and direct testing on the actual lot.

What this tool is good for and what it is not

This page is well suited to quick engineering estimates, classroom demonstrations, training discussions, and early-stage material comparisons. It is not a substitute for a specified test procedure in a contract, a heat-treatment qualification program, or a formal acceptance inspection plan.

Plain-language disclaimer

The hardness conversions provided here are approximate and based on simplified empirical relationships. They are useful for education, preliminary design review, and non-critical engineering judgments. For final certification, regulatory compliance, or safety-critical parts, use official conversion tables and direct hardness testing.

Hardness conversion questions engineers ask