A Brinell hardness number (BHN) and a Rockwell C hardness number (HRC) are two different ways of measuring the same physical property — how resistant a metal is to indentation — and they cannot be compared directly without a conversion table or formula. A hardness conversion calculator that handles BHN to HRC takes a single value on one scale and returns the closest equivalent on the others, following the ISO 18265 standard for metals. The Lizely Hardness Conversion Calculator reads a value you already have and displays the matching HRC, HRB, Vickers and approximate tensile strength as you type.
You will usually land here with a number from a mill test certificate, a quality control log, or an incoming inspection report — and the rest of the document you are filling in expects Rockwell C. The fix is a quick conversion that respects the same ISO 18265 tables metallurgists use in the shop, without pulling out a paper chart or running an empirical formula in a spreadsheet. This guide walks through exactly what the calculator does, how to use it, what the underlying scales mean, and where approximate conversions start to break down.
What Brinell (BHN) and Rockwell C (HRC) Actually Measure
Both numbers describe indentation hardness, but they use different indenters and different loads, which is why the raw values cannot be directly interchanged. Brinell hardness (HB or BHN) presses a hardened steel or tungsten carbide ball — typically 10 mm in diameter — into the surface with a known load, then divides the load by the surface area of the impression. The result is a number that works well on coarse-grained, rough, or non-uniform materials such as cast iron, forgings, and large bars, because the relatively large indent averages out local variations.
Rockwell C (HRC) uses a diamond cone (Brale) indenter and a 150 kgf major load, measuring depth of penetration rather than impression area. It is the dominant scale for hardened tool steels, heat-treated alloys, and finished machined components, where a small, clean indent is essential. Because the geometry is different, a BHN of, say, 300 does not correspond to an HRC of 30 — the two scales barely overlap numerically, even when they describe the same steel.
Why You Need a Hardness Conversion Calculator
Specification sheets rarely use the same scale throughout. A forging drawing may list BHN because the part is rough; a heat-treatment log may list HRC because the surface is finished. Procurement, quality, and design teams routinely have to line up these numbers without re-running the physical test.
The practical reasons you would convert BHN to HRC specifically include:
- Cross-referencing certificates. A supplier reports in HB; your internal spec requires HRC.
- Matching material databases. Many cutting-tool and steel-grade charts are indexed by HRC.
- Estimating tensile strength. ISO 18265 ties HB values on plain-carbon and low-alloy steels to an approximate ultimate tensile strength in MPa or psi.
- Sanity-checking a heat-treat batch. A shop measures BHN on a thick section and wants to know whether the corresponding HRC falls inside the customer window.
How to Convert BHN to HRC With the Calculator
The calculator is built for a specific task: you have one number on one scale and need the equivalent on every other scale. Working through it takes only a moment.
- Open the Hardness Conversion Calculator in your browser.
- Pick the scale you already measured — Brinell (HB), Rockwell C (HRC), Rockwell B (HRB), or Vickers (HV) — from the input scale selector.
- Type the value you have. A small note beneath the field shows the valid table range for that scale, which prevents out-of-range errors.
- Read the equivalent values on the other scales as the page updates — HRC, HRB, Vickers and approximate tensile strength all refresh instantly.
- Copy the HRC figure (or any other scale) directly into your report, drawing, or spreadsheet.
This eliminates the need to invert a lookup table by hand or trust a generic online formula. Because the tool uses the same ISO 18265 source as printed engineering references, the values line up with what your quality team would expect.
Comparing the Hardness Scales at a Glance
Before you rely on a converted number, it helps to know which scale suits which material and which load regime. The table below summarizes the four scales the Lizely calculator handles side by side.
| Scale | Indenter | Typical Load | Best Used For |
|---|---|---|---|
| Brinell (HB / BHN) | 10 mm steel or carbide ball | 500–3000 kgf | Coarse-grained steels, castings, forgings, rough surfaces |
| Rockwell C (HRC) | Diamond cone | 150 kgf | Hardened tool steels, heat-treated components, finished surfaces |
| Rockwell B (HRB) | 1/16 in. steel ball | 100 kgf | Soft steels, brass, aluminum, annealed materials |
| Vickers (HV) | Square pyramid diamond | 1–100 kgf | Laboratory work, thin sections, microhardness surveys, all materials |
The relationship between these scales is monotonic but non-linear, and the exact mapping depends on the material family. For a plain-carbon or low-alloy steel, ISO 18265 provides a tightly defined conversion; for austenitic stainless, high-nickel alloys, or non-ferrous metals, the relationship drifts and conversion tables may warn against direct translation. The calculator applies ISO 18265 because BHN-to-HRC conversions are most reliable on that material family — exactly where the conversion is most often needed.
What Hardness Conversion Means for Tensile Strength
One of the most common downstream uses of a BHN value is estimating ultimate tensile strength (UTS). For plain-carbon and low-alloy steels, ISO 18265 ties Brinell hardness to tensile strength using a well-established proportionality. The Lizely calculator surfaces this estimate alongside the HRC figure so you can answer two questions with one input.
The general direction of the relationship is straightforward: a higher Brinell number corresponds to a higher ultimate tensile strength, and the same monotonic increase carries over to HRC. The exact conversion factors and any shift points should always come from a tabulated reference such as ISO 18265 — which is why the calculator does the lookup for you rather than relying on a single approximate multiplier. For a deeper walkthrough of how Brinell hardness itself is calculated from load, ball, and indent, the guide on calculating Brinell hardness from load, ball and indent gives the full derivation.
Limitations and How to Read the Result
No conversion is exact, and that matters more on BHN-to-HRC than on most other unit translations. The underlying reason is geometric: a Brinell ball indents a wider, shallower area than a Rockwell cone, so the two readings probe slightly different volumes of the same material. Standards like ISO 18265 acknowledge this by publishing tabulated equivalences with permitted tolerances — typically a few HRC points at higher hardness levels.
Treat the output of any hardness conversion calculator as an engineering estimate, not a measurement. Two practical rules of thumb:
- Stay inside the recommended material families. Use the conversion for carbon and low-alloy steels where ISO 18265 applies directly.
- Avoid extrapolating outside the printed range. If your BHN falls at the edge of the ISO table, the converted HRC value becomes noticeably less reliable.
If a drawing calls out a tight HRC window — for instance, 58–62 HRC on a tool-steel punch — the only acceptable way to verify it is a direct Rockwell C test on the part, not a BHN measurement converted across scales.
Putting the Calculator to Work
Once you have used the tool once, the workflow is repeatable. Drop the measured value into the field, read the equivalent, paste it where you need it. For anyone who routinely moves between mill certificates in HB and drawings in HRC, this turns a chart-lookup step into a single keystroke — and keeps the ISO 18265 reference table exactly where metallurgists expect it to live.
Related reading: How to Calculate Hemisphere Volume and Surface Area Instantly.