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Hardness Scale Converter

Converter

Scale Reference

Rockwell C (HRC)

Diamond cone indenter, 150 kgf major load. Standard for hard steels and tool materials.

Valid range: 20–70 HRC

Brinell (HB)

Hardened steel or carbide ball indenter. Results as HBW (tungsten ball).

Valid range: 8–650 HB

All Scales Comparison

Click "Show" to see your hardness value converted to all supported scales at once.

Confidence Key

Exact

Direct table match or same scale.

Interpolated

Value falls between table rows; linear interpolation used.

Extrapolated

Value is outside published table range — treat as estimate.

Approximate

No metals-standard table available (Shore / Mohs); rough estimate only.

About This Tool

Hardness Scale Converter – Rockwell, Brinell, Vickers, Knoop, Shore & Mohs

Hardness is a fundamental material property that engineers, metallurgists, machinists, and quality control inspectors rely on every day. The challenge is that multiple hardness testing methods exist — each with its own scale, indenter geometry, and load — and specifications from different sources rarely use the same scale. A Hardness Scale Converter solves this problem by translating a measured hardness value from one scale into an equivalent value on any other supported scale, using industry-standard correlation data.

Why Are There Multiple Hardness Scales?

Different testing methods were developed for different materials and contexts. The Rockwell test (HRA, HRB, HRC) is fast and produces a direct readout — HRC (diamond cone, 150 kgf) is the standard for hardened steels and tool materials, while HRB (steel ball, 100 kgf) covers softer metals like aluminium and copper alloys.

The Brinell test (HB) uses a hardened steel or carbide ball and is preferred for castings and forgings with coarse grain structure. Vickers (HV) uses a diamond pyramid and covers an exceptionally wide range — from very soft to very hard — making it a popular choice in research and surface engineering. Knoop (HK) uses an elongated diamond pyramid, ideal for thin coatings, ceramics, and brittle materials where minimising indentation size matters.

Shore A and Shore D are spring-loaded polymer scales defined by ASTM D2240, used for rubbers, elastomers, and rigid plastics — a completely different material class from metals. The Mohs scale is a qualitative mineral scratch-resistance ranking (1 = talc, 10 = diamond) used in geology and gemology; it has no linear relationship with indentation-based engineering scales.

How Conversions Are Performed

Because hardness scales measure fundamentally different physical quantities, there is no universal conversion formula. Conversions are instead based on empirically derived cross-reference tables. The primary international standard is ASTM E140 – Standard Hardness Conversion Tables for Metals, which provides correlation data for non-austenitic steel, austenitic stainless steel, and nickel alloys.

This converter uses Vickers (HV) as a universal pivot scale. Any input value is first mapped to an HV equivalent using the ASTM E140 table for the source scale, then the HV value is mapped to the target scale using a second table lookup. For values that fall between published table rows, linear interpolation is applied between the two nearest data points. Each result displays a confidence indicator:

  • Interpolated — the value falls between two table rows; linear interpolation was used. Reliable for most engineering purposes.
  • Extrapolated — the value is outside the published table range. Treat as a rough estimate; direct measurement is recommended.
  • Approximate — no metals-standard table exists (Shore scales, Mohs). The result is a rough estimate based on published correlation curves.

Tensile Strength Estimation

For ferrous metals, hardness correlates statistically with tensile strength. The converter estimates tensile strength using the standard approximation TS ≈ 3.45 × HB (MPa), after first converting your input value to Brinell hardness. This is a statistical approximation, not a material guarantee — heat treatment, alloying elements, and microstructure all affect the actual tensile properties. For critical design decisions, use certified test data rather than hardness-derived estimates.

Limitations to Be Aware Of

All ASTM E140 tables are calibrated for specific material types. Applying steel-based conversion tables to aluminium, copper, titanium, or other non-ferrous alloys introduces error — the correlation between scales shifts depending on alloy composition, heat treatment, and microstructure. Shore A/D conversions to Rockwell or Brinell are especially approximate because they apply to chemically and structurally different materials. The Mohs-to-Vickers mapping is non-linear and should be treated as an order-of-magnitude estimate only.

For quality control, certification, or structural engineering applications, always verify conversions against the applicable ASTM E140 table and, where possible, perform direct hardness measurements on the target scale.

Typical Use Cases

Engineers commonly need to convert steel hardness from HRC to HB when comparing hardness specifications between a customer drawing (in Rockwell C) and a laboratory Brinell test report. Metallurgists use HV to HRC conversions when interpreting microhardness traverse data on hardened components. Procurement teams convert between Vickers and Brinell to verify that raw material certificates meet design requirements. The "Convert to All Scales" view is particularly useful for students and engineers who need to understand the full hardness landscape of a material at a single measurement point.

Frequently Asked Questions

Is the Hardness Scale Converter free?

Yes, Hardness Scale Converter is totally free :)

Can I use the Hardness Scale Converter offline?

Yes, you can install the webapp as PWA.

Is it safe to use Hardness Scale Converter?

Yes, any data related to Hardness Scale Converter only stored in your browser (if storage required). You can simply clear browser cache to clear all the stored data. We do not store any data on server.

How does the Hardness Scale Converter work?

Enter a hardness value, select the source scale (e.g., Rockwell C), and choose a target scale (e.g., Brinell or Vickers). The converter uses Vickers (HV) as a universal pivot: it first maps your input to HV using ASTM E140 correlation tables, then maps HV to the target scale. For values between published table entries, linear interpolation is applied. Results show a confidence indicator — exact, interpolated, or approximate — so you know the reliability of each conversion.

What is ASTM E140 and why is it used here?

ASTM E140 is the internationally recognised standard titled 'Standard Hardness Conversion Tables for Metals.' It provides empirically derived cross-reference tables correlating Brinell, Rockwell (A, B, C), Vickers, Knoop, Shore, and approximate tensile strength values for non-austenitic steel, austenitic stainless steel, and other alloys. Because hardness scales measure different physical phenomena (penetration depth vs. indentation area), there is no universal formula — all conversions rely on these experimentally established tables.

Why do conversion results show 'approximate' for Shore and Mohs?

Shore A and Shore D scales measure rubber and polymer hardness using spring-loaded indenters; they apply to a different material class than the metal-based Rockwell, Brinell, and Vickers scales. Converting between Shore and metal scales is a rough approximation at best. Similarly, the Mohs scale is an ordinal scratch-resistance scale for minerals — it has no linear relationship to indentation depth or force, so Mohs-to-Vickers conversion uses published approximate correlation curves and is inherently less precise.

What is 'Convert to All Scales' and when should I use it?

The 'Convert to All Scales' feature shows your input value simultaneously expressed in every supported scale in one table. Use it when comparing material specifications from different sources or standards (e.g., a supplier provides HV but your internal spec uses HRC and HB), or for educational purposes to understand how different scales relate at a given hardness level.

What is the approximate tensile strength feature?

For ferrous metals (steels, cast iron), hardness correlates empirically with tensile strength. The converter estimates tensile strength in MPa and psi using the approximation TS ≈ 3.45 × HB, after first converting your input to Brinell (HB). This is a statistical approximation valid for non-austenitic steel and should not replace direct tensile testing for critical engineering applications.

Are conversions valid for all metals and alloys?

The conversion tables are calibrated primarily for non-austenitic steel (the most common engineering material). Conversions for aluminium, copper, stainless steel, titanium, or other non-ferrous alloys will differ — sometimes significantly — from the tabulated steel values. The tool flags out-of-standard-range values and recommends treating cross-material conversions as estimates. For critical specifications, consult the ASTM E140 tables for the specific material class.