How accurate are hardness conversions?

Conversions between hardness scales are approximate by nature because each test measures resistance to a different indenter under a different load. The ASTM E140 tables used here are the industry standard for carbon and low-alloy steel, and interpolating between rows keeps the error small, but treat the result as a reliable estimate rather than an exact measurement.

Why is a value sometimes shown as out of range?

Each hardness scale has a practical span. Rockwell C is meaningful for hardened steel from roughly 20 to 68 HRC, while Rockwell B suits softer material below about 100 HRB. If your input or its equivalent falls outside the valid window of a scale, the tool flags it rather than guessing a meaningless number.

Can I convert hardness to tensile strength?

For steel there is a well-established empirical link, so the tool estimates tensile strength in ksi and MPa from the Vickers value. This relationship does not hold for non-ferrous metals or stainless steel, and it is only an approximation even for steel, so do not use it for design without test data.

Do these conversions work for stainless steel or aluminum?

No. ASTM E140 has separate tables for austenitic stainless, nickel alloys, and other materials, and the scale relationships differ. This calculator uses the carbon and low-alloy steel table, so do not apply its numbers to stainless, aluminum, brass, or case-hardened surfaces.

What is the difference between Vickers and Brinell?

Vickers uses a diamond pyramid indenter and a small load, giving one continuous scale across soft and hard metals, which is why it works well as a master scale. Brinell presses a hardened ball under a heavy load and reads the indentation diameter, which suits coarse or non-uniform materials but flattens out on very hard steel.

What is the Hardness Conversion Calculator?

Convert metal hardness between HRC, HRB, HRA, Brinell (10mm/3000kgf), and Vickers, plus an estimated tensile strength in ksi and MPa, using ASTM E140 conversion tables for steel. Out-of-range values are flagged for each scale. It runs free in your browser on Gera Tools, with nothing uploaded.

Hardness Conversion Calculator

Name: Hardness Conversion Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Hardness is measured several different ways, and shop drawings, mill certificates, and heat-treat specs rarely all use the same one. This calculator translates a value on one scale into its equivalents on the others for steel, so you can compare an HRC spec against a Brinell reading or a Vickers test without hunting through a printed chart.

The four scales and what each measures

Understanding what each test actually does clarifies why the conversions are approximate rather than exact.

Rockwell C (HRC) presses a diamond cone (Brale indenter) into the surface under a 150 kgf major load and measures the depth of penetration. It is fast, non-destructive for most parts, and covers the hardened-steel range from roughly 20 to 68 HRC. It is the most common scale on heat-treat specifications for tool steels, dies, and case-hardened components.

Brinell (HB or HBW) presses a 10 mm tungsten carbide ball under 3,000 kgf and measures the diameter of the resulting indentation. Because it uses a large indenter, it averages over a wider area and is better for inhomogeneous materials like cast iron and forgings. The test leaves a visible dent, and the scale tops out around 650 HB before the ball starts to deform.

Vickers (HV) uses a diamond pyramid under a small load (often 1–100 kgf) and measures the diagonal of the impression. Because the geometry is self-similar — the impression shape does not change with load — Vickers values are comparable across loads. This makes it the preferred master scale for conversion tables and for testing thin material, coatings, and case depths.

Rockwell B (HRB) uses a 1/16-inch steel ball under 100 kgf and suits softer materials (annealed steel, aluminium alloys, brass) in the range 0–100 HRB. Once a material hardens beyond 100 HRB it should be measured on the C scale instead.

How it works

Each hardness test pushes a different indenter into the surface under a different load, so there is no exact algebraic formula linking them. Instead, the industry relies on measured correlation tables. ASTM E140 publishes those tables for carbon and low-alloy steel, and this tool stores a condensed version with Vickers as the master column.

input value  ->  interpolate to Vickers (HV)
HV           ->  interpolate to HRC, HRB, HRA, HB
HV           ->  estimate tensile strength (ksi, then MPa)

When you enter a value, it is first converted to Vickers by linear interpolation between the nearest table rows, then Vickers is interpolated back out to every other scale. Any scale whose valid window does not include your value is marked out of range rather than extrapolated.

Hardness to tensile strength

For carbon and low-alloy steel there is a well-established empirical relationship between hardness and tensile strength. The tool uses the Vickers value to estimate tensile strength in both ksi and MPa. Treat this as a useful cross-check — for example, verifying that a hardness reading is consistent with a stated strength class — not as a replacement for a tensile test. The relationship does not hold for stainless steel, aluminium, or surface-treated parts.

Tips and limitations

These conversions apply only to carbon and low-alloy steels measured in the bulk material. Stainless steel, nickel alloys, and non-ferrous metals follow different correlation tables from ASTM E140 not included here. Case-hardened surfaces have a steep hardness gradient with depth that single-point conversion cannot capture. For acceptance testing, always measure on the scale your specification calls out rather than converting from another.