Rockwell Hardness Conversion Calculator

Material family: The metal group used to choose the right conversion table, such as non-austenitic steel, austenitic stainless steel, copper alloys, nickel alloys, or aluminum alloys.

Measured hardness scale: The scale your original test used, such as HRC, HRB, HRA, HV, HBW, HK, or a superficial Rockwell scale.

Measured hardness value: The number you already have from the hardness test report.

Target hardness scale: The scale you want the result shown in.

Conversion status: A result tag that tells you whether the number is a same-scale pass-through, exact table value, interpolated estimate, unsupported, or outside supported range.

Standards basis: The table source used for the conversion, such as ASTM E140 or ISO 18265. ASTM E140 is a hardness conversion table standard for metals [1].

Between-table method: How the calculator handles values between listed rows. Linear interpolation estimates between two nearby table points, while exact-only returns a result only for listed rows.

Nearest table points used: The two source rows that bracket your input when interpolation is used.

Estimated tensile strength: An approximate strength value derived from supported table relationships, shown in ksi and MPa when available.

Mistake: Picking the wrong Material family because the part is steel-like or stainless-like.
Fix: Match Material family to the actual alloy group used by the conversion table. A wrong family can change Converted hardness and Conversion status .

Mistake: Confusing Measured hardness scale with Target hardness scale , especially HRC vs HRB or superficial scales like HR15N.
Fix: Recheck both labels before calculating, and verify the reported Target scale in the results.

Mistake: Entering a between-row value such as 60.5, then using Between-table method set to exact rows only.
Fix: Switch Between-table method to linear interpolation if you want an estimate, or enter a listed table row value if you need an exact-table result.

Mistake: Treating an interpolated Converted hardness as if it were a direct measured test value.
Fix: Read Conversion status . If it says interpolated estimate, use it as an approximation and not as a replacement for a direct hardness test.

Mistake: Ignoring the Valid range note when the Measured hardness value is outside the table range.
Fix: If the result says outside supported range, do not extrapolate. Use a hardness scale and material family that are covered by the standard table.

Mistake: Turning on Show tensile strength estimate when supported and assuming it is always available.
Fix: Check Estimated tensile strength and Source standard used . If tensile strength is not supported for that selection, treat it as unavailable rather than missing math.

• Results are table-based conversions, not direct physical measurements. They should not replace a real hardness test on the target scale.
• Conversions depend on Material family. Using the wrong family can make a result look precise while still being wrong.
• If the chosen source and target pair is not supported for the selected material family or standard, the calculator should report the path as unavailable rather than guess.
• If Measured hardness value is outside the covered table range, the calculator does not extrapolate beyond the table.
• When Between-table method is linear interpolation, the result is an estimate between listed rows, not an exact table entry.
• Different standards can have different supported ranges or available conversion paths, so changing Standards basis can change both the result and whether a result is available.
• Estimated tensile strength is only shown when the selected standard and material family support that relationship, and it remains approximate even when available.
• Rockwell scale names matter. HRC, HRB, HRA, and superficial scales such as HR15N or HR30T are not interchangeable.

How the calculator converts hardness

The tool follows a standards-first lookup method. It first uses Material family, Measured hardness scale, Target hardness scale, and Standards basis to find the correct conversion table. Hardness conversion standards are table-based rather than one universal equation [3].

If input_value equals a listed table source value, output_value = corresponding listed destination value.

If your entered value exactly matches a table row, the calculator returns that row's destination value and marks Conversion status as an exact table value.

Interpolation between listed rows

If your value falls between two valid source rows and Between-table method is set to linear interpolation, the tool estimates the destination value from the two nearest points.

output = y1 + (input - x1) * (y2 - y1) / (x2 - x1)

Here, input is your entered source hardness, x1 and x2 are the nearest source-table values around it, and y1 and y2 are the matching destination values. The result is tagged as an interpolated estimate, and Nearest table points used shows the bracketing rows.

Same-scale and unavailable cases

If Measured hardness scale and Target hardness scale are the same, the calculator returns the original number with a same-scale status. If the path is unsupported for the selected material family, or if the value is outside the supported table range, it returns no conversion instead of extrapolating. In exact-only mode, a between-row input returns exact table row not found.

Tensile strength estimate

When the selected table supports it and you turn on Show tensile strength estimate when supported, the calculator reports an approximate tensile strength in both ksi and MPa.

MPa = ksi * 6.894757293168

This is only a unit conversion from ksi to MPa. The hardness-to-strength relationship itself is still an approximation from the table relationship, not a substitute for a direct tensile test.

Mini example

Suppose you choose non-austenitic steel, set Measured hardness scale to HRC, enter 60, and convert to HV. If 60 HRC is a listed table row under the selected standard, the calculator returns the matching HV value as an exact table result. If you enter 60.5 and use linear interpolation, it finds the two nearest HRC rows, estimates the HV value between them, and labels the result as interpolated instead of exact.

Assumptions behind the result

The method assumes the selected standard contains a valid table for the chosen material family and scale pair, and that your original hardness measurement was taken and reported on the stated scale. Rockwell testing itself is governed by a separate test-method standard, ASTM E18 [2]. Industry guidance also warns that hardness conversions are material dependent and should be used carefully rather than treated as perfectly exact [2].