What is the difference between hardness scales?

HRC (Rockwell C) uses a diamond cone indenter with 150 kgf load, suitable for hardened steels (20-70 HRC). HRB (Rockwell B) uses a 1/16" steel ball with 100 kgf, for softer materials (20-100 HRB). HV (Vickers) uses a diamond pyramid with variable load, suitable for all ranges. HB (Brinell) uses a 10 mm carbide ball with 3000 kgf load, best for castings and softer steels.

When should I use which hardness scale?

Use HRC for hardened and tempered steels above ~20 HRC. Use HRB for annealed and softer steels below ~100 HRB. Use HV for thin materials, coatings, case-hardened surfaces, and when a wide range is needed. Use HB for castings, forgings, and when a large test area is acceptable.

Why are hardness conversions approximate?

Different hardness tests use different indenters, loads, and measurement methods. The relationship between scales is not purely mathematical but empirical, based on testing many material samples. ASTM E140 provides accepted conversion tables, but exact conversions depend on the specific material, its condition, and microstructure.

How do I estimate tensile strength from hardness?

For carbon and alloy steels, a common approximation is Rm (MPa) ≈ 3.45 × HB. This is a rough estimate valid for steels in the range of approximately 100-400 HB. For stainless steels, non-ferrous metals, or very hard steels, this relationship does not apply accurately.

What test methods do these scales use?

Rockwell (HRC/HRB): measures depth of indentation under a specific load. Quick and portable. Vickers (HV): measures diagonal of a diamond pyramid indentation under variable load. Very precise, works for all hardness ranges. Brinell (HB): measures diameter of a ball indentation under high load. Good for averaging over larger areas (castings, welds).

Free Engineering Tool

Hardness Converter

Convert between Rockwell HRC, Brinell HB, Vickers HV, and Rockwell HRB hardness scales. Based on ASTM E140 conversion data with linear interpolation.

ASTM E140 HRC ↔ HB ↔ HV Tensile Strength

Results

HRC (Rockwell C)

—

HRC (Rockwell C)

—

HB (Brinell)

—

HV (Vickers)

—

HRB (Rockwell B)

—

Approx. Tensile Strength Rm (steel)

—

Rm ≈ 3.45 × HB (approximate, for carbon & alloy steels)

HRC Range (Hardened Steels)

HRC	HV	HB	Rm (MPa)
20	238	228	~787
25	255	243	~838
30	279	266	~918
35	331	311	~1073
40	392	360	~1242
45	458	421	~1452
50	542	484	~1670
55	595	544	~1877
60	697	—	—
65	832	—	—

HRB Range (Softer Steels)

HRB	HV	HB	Rm (MPa)
60	107	105	~362
70	120	118	~407
80	141	138	~476
90	171	166	~573
100	210	202	~697

ℹ️ Note: Values between table entries are calculated using linear interpolation. HB values above HRC 55 are typically not measured (material too hard for ball indenter). Tensile strength estimates apply to carbon and alloy steels only.

Rockwell Hardness (HRC / HRB)

The Rockwell test measures the depth of penetration under a large load compared to a preload. It is fast, easy, and widely used in production.

HRC — Diamond cone (Brale) indenter, 150 kgf major load. Range: 20–70 HRC. For hardened steels.
HRB — 1/16″ steel ball, 100 kgf major load. Range: 20–100 HRB. For softer steels, brass, aluminum.

Vickers Hardness (HV)

Uses a diamond pyramid indenter with variable load (1–120 kgf). Measures the diagonal of the indentation. Works for all hardness ranges from very soft to very hard.

Brinell Hardness (HB)

Uses a 10 mm tungsten carbide ball with 3000 kgf load (for steel). Measures the diameter of the indentation. Best for coarse-grained materials like castings.

Tensile Strength Approximation

⚠️ Important: The Rm ≈ 3.45 × HB relationship is approximate and only valid for carbon and alloy steels in the range ~100–400 HB. Do not use for stainless steels, cast irons, non-ferrous metals, or hardened steels above ~55 HRC.

Practical Example

Example — Quenched & Tempered Steel

Given: Measured hardness = 45 HRC

From ASTM E140 table: HRC 45 ≈ HV 458 ≈ HB 421

Estimated tensile strength: Rm ≈ 3.45 × 421 = ~1452 MPa