How to use the converter
- Enter the measured hardness in Value (for example, 250 if the report says 250 BHN, or 60 if it says 60 HRC).
- Select the scale the value is currently reported in under From Scale.
- Select the desired output scale under To Scale.
- Select Convert. The result appears in the results panel and can be copied with Copy Result.
Tip for repeatability: if you are comparing multiple materials, keep a small note of the input value, the source scale, and the target scale. That makes it easy to reproduce the same conversion later and reduces the chance of mixing up HRB and HRC.
Common hardness scales (what the symbols mean)
Hardness numbers are dimensionless values derived from indentation tests. The number you see depends on the test method, not only on the material. The four scales in this converter are widely used in metalworking and inspection.
- BHN (Brinell) — ball indenter; often used for castings, forgings, and general steel hardness checks. Brinell is popular when the surface is relatively rough or when a larger indentation is acceptable.
- HV (Vickers) — diamond pyramid; common in labs and for microhardness. Vickers can be used across a wide range of loads, which makes it useful for thin sections and metallographic work.
- HRB (Rockwell B) — ball indenter with lighter load; typical for softer metals, mild steels, and some non-ferrous alloys. HRB is often used when HRC would be too low to be meaningful.
- HRC (Rockwell C) — diamond cone (Brale) with higher load; typical for harder steels, tool steels, and case-hardened surfaces. HRC is commonly referenced in heat treatment specifications.
Because each method uses different loads and indenters, two materials with the same BHN do not necessarily have the same HRB or HRC relationship if their microstructures differ significantly. That is why published conversion charts are usually material-family specific.
Model and formulas used (empirical)
The calculator uses Brinell hardness (BHN) as an internal reference. It first converts the input scale to an approximate BHN value, then converts BHN to the target scale. This two-step approach keeps the logic consistent and mirrors how many quick-reference charts are organized.
Conversions to BHN (internal step):
- From BHN: BHN = BHN
- From HV: BHN ≈ HV / 0.95
- From HRB: BHN ≈ 4.7 × HRB + 20
- From HRC: BHN ≈ 9.5 × HRC + 70
Conversions from BHN (output step):
- To HV: HV ≈ 0.95 × BHN
- To HRB: HRB ≈ (BHN − 20) / 4.7
- To HRC: HRC ≈ (BHN − 70) / 9.5
These linear relationships are commonly used as quick estimates for many carbon and low-alloy steels in mid ranges. They are not a substitute for ASTM/ISO conversion tables, which may use piecewise curves and material-specific datasets.
Example formula (MathML)
One of the relationships used is the approximate conversion from Brinell to Rockwell C:
Worked examples (step-by-step)
Worked examples help you confirm that you selected the correct scale and that the magnitude of the result makes sense.
The examples below use the same formulas as the calculator, so you can reproduce them by entering the same inputs.
Example 1: Convert 250 BHN to HV, HRB, and HRC
Suppose a supplier datasheet lists a steel at 250 BHN. You want to compare it to a specification written in Vickers or Rockwell.
- To HV: HV ≈ 0.95 × 250 ≈ 237.5 → about 237.5 HV (the calculator rounds to one decimal place).
- To HRB: HRB ≈ (250 − 20) / 4.7 ≈ 230 / 4.7 ≈ 48.9 HRB.
- To HRC: HRC ≈ (250 − 70) / 9.5 ≈ 180 / 9.5 ≈ 18.9 HRC.
Interpretation: values around 15–25 HRC are typical for many medium-strength steels. If you expected a hardened tool steel, this would be too low, which is a clue to re-check the material condition (annealed vs quenched-and-tempered) or the source report.
Example 2: Convert 60 HRC to BHN and HV
Now consider a hard tool steel measured at 60 HRC. The internal step is to estimate BHN first:
- HRC to BHN: BHN ≈ 9.5 × 60 + 70 = 570 + 70 = 640 BHN.
- BHN to HV: HV ≈ 0.95 × 640 = 608 HV.
Interpretation: a BHN in the 600+ range is consistent with very hard, wear-resistant steels. If you see a much lower BHN after converting from a high HRC, it often indicates the wrong source scale was selected (for example, HRB instead of HRC).
Example 3: Common mistake check (HRB vs HRC)
Rockwell B and Rockwell C are easy to confuse because both are reported as “HR” values. However, they apply to different hardness ranges.
As a quick check: 90 HRB is a plausible value for mild steel, while 90 HRC is generally not realistic for steel.
If you accidentally convert 90 as HRC, the internal BHN estimate becomes BHN ≈ 9.5 × 90 + 70 = 925, which is outside typical steel ranges and should trigger a re-check.
Sanity checks and typical ranges (rule-of-thumb)
Use these broad bands to catch obvious input mistakes. They are general guidelines for steels and similar alloys; your specific alloy, heat treatment, and test method can shift the expected range.
- BHN: ~120–220 (mild/structural steels), ~250–350 (many stronger steels), up to ~600+ (very hard tool steels/surfaces)
- HV: ~130–700 common for many engineering steels; microhardness on coatings can be higher
- HRB: ~40–100 for softer metals and mild steels; above this, HRC is often used
- HRC: ~20–40 (many quenched-and-tempered steels), ~50–65 (tool steels/case hardened)
Another sanity check is directionality: if you convert a value from a “harder” scale range to a “softer” scale range, the number may increase or decrease depending on the scale definition. What matters is whether the result lands in a plausible band for the material condition.
Reference table (approximate conversions from BHN)
The table below shows representative conversions using the same formulas as the calculator. Small differences versus published charts are normal because many charts use non-linear fits and material-specific datasets.
This converter is intentionally simple so it can be used quickly. That simplicity comes with assumptions. If you understand them, you can use the output appropriately.
Good for: quick engineering estimates, translating between drawing conventions, classroom demonstrations, and early-stage material selection.
Not for: replacing a specified test method, qualifying heat treatment processes, or accepting/rejecting safety-critical parts without additional verification.
