Rockwell Hardness Conversion Calculator - HRC, HRA, HRB

The rockwell hardness conversion calculator reads a single measured value on the HRC, HRA, or HRB scale and reports equivalent HRC, HRA, HRB, Brinell HBW, Vickers HV, Knoop HK, and approximate tensile strength. It supports materials-testing, manufacturing, and mechanical-engineering workflows where a certificate, drawing, or supplier report uses a different scale than the receiving team records.

• • Reconcile a certificate against a drawing: Use it when a heat-treat certificate reports HRC but the drawing lists Brinell, or a supplier datasheet quotes HV and the inspection plan calls for HRC.
• • Estimate tensile from a single HRC reading: Read a measured HRC, look up the implied Brinell, and apply the standard 3.45 * HBW relationship for a planning-level tensile in megapascals.
• • Compare scales on thin or hard sections: Pick HRA or HRB when the coupon is too thin or too soft for HRC, and read the equivalent HRC, HBW, HV, and HK from the same reference table.

Rockwell hardness is a family of indentation tests using a diamond cone or steel ball pressed into the surface under a defined load. The HRC, HRA, and HRB scales are the three most common in steel work, and converting between them is routine in material review, heat-treat verification, and supplier acceptance.

When the same steel part needs Brinell, Vickers, and Rockwell in one panel, the Hardness Conversion Calculator covers the cross-scale comparison for a single source scale.

The calculator holds a steel reference table published in ASTM E140 and ISO 18265, with one row per integer HRC value from 20 to 65 and a paired HRA, HBW, HV, HK, and tensile value for each row. HRA and HRB inputs first resolve to an implied HRC via a small sub-table, then the same linear interpolation runs across the master HRC table.

• hardnessValue: Measured value entered on the source scale (HRC, HRA, or HRB).
• sourceScale: Source Rockwell scale identifier: HRC, HRA, or HRB.
• HRC master row: Paired table row with HRA, HBW, HV, HK, and tensile values for one HRC integer.
• implied HRC: HRC value derived from HRA or HRB via the sub-table.

ASTM E140 warns that converted values are approximate, the same wording carried into ISO 18265. The calculator reflects that by interpolating between printed rows and clamping out-of-range inputs to the nearest valid row before emitting nulls for scales that are not physically meaningful. The approximate tensile uses the standard 3.45 * HBW relationship, rounded to the nearest 10 MPa as is common in materials references.

According to ASTM E140, hardness conversion tables are approximate and apply only to the materials indicated in each table, so converted Rockwell values should be treated as engineering estimates rather than as a replacement for a specified test.

The equivalent HBW feeds into a strength check, and the Beam Bending Stress Calculator returns the bending stress on the gross cross-section.

Four ideas explain why the calculator returns equivalent scales in one view and why some rows are marked outside the supported range.

HRC handles quenched and tempered steels from 20 to 65, HRA handles thin sheets, carburized cases, and very hard surfaces that the heavier HRC load would damage, and HRB handles annealed steels and other soft metals that would not register a meaningful HRC value. The implied HRC is the common reference frame so every output column traces back to one published row.

The hardness-derived peak stress is the starting point for a stress concentration review, and the Stress Concentration Factor Calculator applies the peak-to-nominal ratio on the same section.

Enter the measured value and the scale it was recorded on, then read the equivalent scales, Brinell, Vickers, Knoop, and approximate tensile in one view.

1. 1 Enter the measured value: Type the number from the certificate, drawing, or inspection report. Decimals are accepted so values between printed table rows can be tested.
2. 2 Pick the source scale: Choose HRC for hardened steels, HRA for thin or hard sections, or HRB for softer steels and annealed stock.
3. 3 Read the equivalent scales: The results panel shows HRC, HRA, HRB, HBW, HV, and HK in one table. A null result with an outside-range note means the implied HRC is outside the master table.
4. 4 Check the tensile strength: The bottom row reports the approximate tensile in megapascals from the equivalent Brinell. Treat it as a planning reference, not a replacement for a tensile test.
5. 5 Compare against the controlled document: Use the equivalent scale to check whether the reading meets the limit named on the drawing or order. If close to a limit, retest on the scale named in the specification.

A heat-treat certificate reports 32 HRC and the drawing lists 290 HBW minimum. Enter 32 and pick HRC. The calculator returns 318 HBW, which is above 290 HBW so the part passes the equivalent-scale check. The drawing-specified HRC test should still be re-run for acceptance.

Once the equivalent HBW and approximate tensile are in hand, the Factor of Safety Calculator applies the same material strength against the working load.

The calculator keeps the most common cross-scale comparisons in one panel so a single entry covers every reported hardness reading on a steel part.

• • Three source scales, one panel: HRC, HRA, and HRB share the same input row and the same results table, so a user does not need to switch tools when the source scale changes between suppliers.
• • Approximate tensile included: The bottom row reports the standard 3.45 * HBW relationship, the most cited planning shortcut for steel context.
• • Interpolated between printed rows: Values that fall between ASTM E140 table rows are linearly interpolated, so a 35 HRC reading returns the same mid-table values a hand calculation would give.
• • Range guards instead of misleading numbers: Inputs outside the supported range return null with an outside-range note, safer than silent extrapolation.
• • Pairs with material and strength reviews: The equivalent Brinell is the right input for fatigue, factor-of-safety, and stress-concentration reviews that follow.

The biggest practical win is the link between a single measured value and every other scale the same lot of steel is likely to be reported on. A drawing may list Brinell, a certificate HRC, and a lab HV; the calculator keeps all three in one view for any of them without a separate hand calculation.

Four inputs move the result more than the math, and two limitations matter before a converted value is treated as a final design number.

• • The master table is approximate and applies only to the material family it was built for. Conversion should not replace a test on the scale named in the controlled document, especially near acceptance limits.
• • The Brinell-to-tensile relationship is a planning shortcut. Material standards and order specifications should rely on a tensile test when the result is part of acceptance or design verification.

A 40 HRC reading is the same HRC value whether the part is a precision-ground tool block or a hot-rolled bar, but the equivalent Brinell and Vickers can shift by a few percent depending on the material family. ISO 18265 publishes separate tables for unalloyed, low-alloy, high-alloy steels, and non-ferrous metals so the converted value can be refined.

According to ISO 18265, conversion between hardness scales is material-dependent and the standard publishes separate conversion tables for unalloyed, low-alloy, high-alloy steels, and non-ferrous metals.

According to Wikipedia's summary of the Brinell scale, the approximate tensile-strength relationship for steel is tensile_strength_MPa approximately equal to 3.45 multiplied by HBW, the multiplier the calculator uses.

A converted hardness reading is the right input for a fatigue check, and the Fatigue Life Calculator turns the equivalent peak stress into a cycle count.