An accurate hardness conversion calculator for steel is built on the published ASTM E140 / SAE J417 conversion table and returns equivalent values across Rockwell C (HRC), Rockwell B (HRB), Vickers (HV), and Brinell (HB) the moment a number is typed in. This tool turns one measured hardness reading into every other scale on the chart, plus an approximate ultimate tensile strength in both MPa and ksi, by interpolating between the standard anchor rows that appear in the ASTM E140 table for non-austenitic carbon and low-alloy steel. Because the relationship between any two scales is empirical — not a closed-form equation — accuracy depends on starting from a calibrated table and never extrapolating past its ends. The calculator shows the valid input range beneath each field and clearly returns "out of range" or "not defined" rather than inventing values for hardnesses that fall outside the supported scale. Entering HRC 60, for example, lands directly on a published anchor and returns HV 697 and HB 654 immediately, while a value such as HRC 47 sits between anchors and is interpolated proportionally from the surrounding rows. Because nothing leaves your browser, the lookup stays fast and private and the answer updates as you type.
The Four Hardness Scales This Calculator Handles
Steel hardness is reported on four common scales, each using a different indenter and load. The calculator treats all four as valid inputs and converts between them so you can read every equivalent at once.
- Rockwell C (HRC) uses a diamond cone indenter under a 150 kgf load and is the standard scale for hardened steels. It is well-defined from roughly HRC 20 to HRC 68 and saturates outside that range.
- Rockwell B (HRB) uses a 1/16 inch steel ball under a 100 kgf load and is used for softer steels, generally up to about HRB 100. It barely overlaps with HRC.
- Vickers (HV) presses a diamond pyramid and is defined across the full hardness range, which is why most published conversion tables treat HV as the backbone when moving between scales.
- Brinell (HB) presses a 10 mm ball under 3000 kgf. It is widely quoted from about HB 100 to HB 650; above roughly HB 650 a tungsten-carbide ball (HBW) is required.
If you need to compute Brinell hardness directly from a measured indentation rather than a converted value, the Brinell Hardness Calculator works from load, ball diameter, and indent diameter.
Converting Hardness Scales Step by Step
The conversion process is the same whether you start from HRC, HRB, HV, or HB. Pick the scale you already have, type the number, and read off the equivalents as the result updates.
- Choose the input scale. Select Rockwell C (HRC), Rockwell B (HRB), Vickers (HV), or Brinell (HB) from the input selector — whichever one your hardness tester produced.
- Type the value you measured. Enter the number into that field. The valid range for the chosen scale is shown directly beneath the field so you can confirm your reading is supported.
- Read the equivalents as the field updates. The HRC, HRB, HV, and HB values, plus an approximate ultimate tensile strength in MPa and ksi, recalculate as you type — there is no submit button.
- Check for out-of-range or not-defined markers. If the calculator returns "out of range" or "not defined" on a scale, that scale is not valid at your hardness. For example, Rockwell C is undefined for very soft steel and Rockwell B saturates near 100.
- Confirm against the right material. The numbers are calibrated for non-austenitic carbon and low-alloy steel, so for other metals treat the result as a rough guide and re-measure on the actual scale when the value drives a decision.
Why a Lookup Table, Not a Formula
Hardness tests measure slightly different combinations of material behavior — depth of penetration under load, diameter of an impression, the optical diagonal of a pyramid indent. Because of that, no exact closed-form equation links one scale to another; conversion tables are inherently empirical. They are built by testing the same specimens on multiple machines and recording the readings, then publishing the results as anchor points across the full range.
The Hardness Conversion Calculator stores discrete anchor rows from a published steel conversion table and linearly interpolates between them. Hit a value that lands exactly on an anchor and you get the standard published number; land between anchors and the tool estimates proportionally; go past the end of a scale and the tool clearly says out of range rather than extrapolating. This approach is what makes the calculator accurate within the calibrated range and honest outside it — it never invents numbers it cannot support.
ASTM E140 Anchor Values Used for Accurate Conversion
The anchor rows built into the calculator come from the ASTM E140 and SAE J417 conversion tables for non-austenitic carbon and low-alloy steel. The same numbers appear in engineering references worldwide, so a value you read in a datasheet will line up with what the tool produces. A small selection of the published anchor points:
| Rockwell C (HRC) | Vickers (HV) | Brinell (HB) | Rockwell B (HRB) |
|---|---|---|---|
| 20 | 238 | 222 | 97 |
| 40 | 392 | 371 | — |
| 60 | 697 | 654 | — |
Values between those anchors are interpolated proportionally from the surrounding rows, which keeps intermediate readings consistent with the table's resolution. For HRC values between published anchors, the calculator interpolates linearly rather than using a fabricated figure, and for hardnesses outside a scale's supported range it returns "out of range" or "not defined" instead. The tensile-strength estimate is drawn from the same table so for carbon and low-alloy steel the MPa and ksi numbers track published data closely.
Material Types and Conversion Limits
The ASTM E140 / SAE J417 tables are calibrated for non-austenitic carbon and low-alloy steel, which is the same scope the calculator is built for. Other common metals follow different hardness relationships, and a converted number for them can be off by a wide margin.
- Austenitic stainless steel work-hardens under the indenter, so a Brinell reading does not translate to the same HRC value as it would on mild steel.
- Tool steel and high-speed steel have their own published conversion tables; generic steel anchors will drift at the high end of the range.
- Cast iron varies with graphite content and grain structure, so the same converted value should not be trusted for design decisions.
- Non-ferrous metals such as aluminum, copper, and brass sit on much softer hardness ranges and are not covered by the table at all.
The practical rule is to treat any conversion as an estimate and to measure on the actual scale whenever the value drives a design, safety, or acceptance decision. When the answer must be exact, run the test on the scale your spec calls for rather than relying on a converted number.
Reading the Tensile Strength Estimate
For carbon and low-alloy steel, ultimate tensile strength tracks hardness closely enough to give a useful estimate. The calculator shows that estimate in MPa and ksi alongside the converted hardness values, using the same empirical table the conversions come from. It is meant as a quick sanity check, not as a replacement for a real tensile test.
If the part is critical — a structural weld, a fastener, a heat-treated tool — keep the tensile-strength figure as a guide and run an actual tensile test on a representative sample. Hardened surfaces, thin sections, and case-hardened parts in particular can read high on a hardness test but behave very differently under tension, so the estimate is the least reliable output the tool produces and should never be cited in place of measured strength.
Get an Accurate Conversion in One Step
Open the Hardness Conversion Calculator, pick the scale you already know, type the value, and read off every equivalent hardness plus an approximate tensile strength as the result updates in real time. Because nothing is uploaded, the lookup is private and reproducible on the same input every time you run it.