Hardness Converter

Material hardness is measured using different scales depending on the application. There is no exact mathematical formula between scales; conversions are based on empirical data.

Common hardness scales:

• Rockwell C (HRC), most common for hardened steel, usable from about 20 to 65
• Brinell (HB), widely used for softer metals and raw stock, and unreliable above about 650
• Vickers (HV), versatile, works on all materials including thin coatings

Approximate conversion table (for steel):

These are the numbers the calculator above uses. Values between the rows are interpolated, and nothing outside this range converts at all.

Hardness to tensile strength:

For ordinary carbon and alloy steel there is a rough but genuinely useful shortcut: ultimate tensile strength in megapascals is about 3.45 times the Brinell number, which in imperial terms is 500 psi per Brinell point. A 200 HB shaft is therefore around 690 MPa, or 100 ksi. Within about ten percent that holds up to roughly 400 HB. Past that, near 43 HRC, it falls apart, because the steel has stopped failing in a ductile way and hardness no longer tracks strength. Above 400 HB a hardness number is telling you about wear resistance, not about how much load the part will take.

Mohs scale measures scratch resistance (1–10). It is mainly used for minerals, not metals.

• 1 = Talc, 5 = Glass, 7 = Quartz, 10 = Diamond

Note: Conversions between hardness scales are approximate. They vary depending on the specific material being tested.

Why so many scales for one property? Because each test presses a different indenter into the surface under a different load, and each suits a different job. Rockwell is fast and reads straight off the machine, which is why it rules the shop floor. Brinell uses a large ball that averages over a wide area, ideal for coarse or uneven material like castings. Vickers presses a diamond pyramid and works on everything from thin platings to the hardest steel, so labs favor it for precision. They’re all measuring the same idea of resistance to denting, just by slightly different physical means.

That difference is exactly why the conversions are only ever approximate. A cross-reference table like the one above holds well for ordinary carbon and alloy steels, the material it was built from, but drifts for stainless, aluminum, or case-hardened parts whose surface behaves differently from their core. There’s also a range issue: Rockwell C is meant for hard material and becomes unreliable on soft metals, where you’d switch to the Rockwell B scale or Brinell instead. Treat a converted number as a close estimate for specifying or comparing, not as a substitute for testing on the scale that actually matters.