Hardness Conversion Calculator

Q: What is 55 HRC in Brinell and Vickers?

55 HRC is about 595 HV and about 560 HB . It also lines up with roughly 1830 MPa (265 ksi) of tensile strength in steel. These numbers come from the ASTM E140 tables for carbon and alloy steel. Treat them as close matches, not exact swaps.

Q: What is the hardest steel on the Rockwell C scale?

Most published conversion tables stop near 68 HRC , which is about 940 HV. Fully hardened tool steels like M2, D2, and some powder metal grades land in the 60 to 66 HRC range. Above 68 HRC the Rockwell C test loses meaning because the diamond cone barely moves. Labs switch to Vickers or Knoop for those cases.

Q: What hardness should a knife blade be?

Most kitchen and pocket knives run 56 to 62 HRC . 56 to 58 HRC: tougher, easier to sharpen, chips less. Good for choppers and outdoor knives. 59 to 62 HRC: holds an edge longer but is more brittle. Common in Japanese kitchen knives. Above 63 HRC: very long edge life, but the tip can snap.

Q: How hard is 6061-T6 aluminum?

6061-T6 is about 95 HB or roughly 60 HRB . In Vickers that is close to 100 HV. Aluminum is far too soft for Rockwell C. Use HRB, Brinell, or Vickers. Also skip the hardness to tensile rule, since it was built for steel.

Q: Which hardness test should I use on thin parts or coatings?

Use Vickers (HV) or Knoop (HK) . Both use tiny loads and leave small dents. A good rule: the part must be at least 10 times thicker than the dent depth. Rockwell C and Brinell make deep, wide dents that push through thin sheet and read the backing plate instead of the part.

Hardness Conversion Calculator

Introduction

This hardness conversion calculator changes one hardness number into all the others. Type a value in Rockwell C (HRC), Rockwell B (HRB), Vickers (HV), Brinell (HB), Knoop (HK), or Shore A and D. The tool shows the matching numbers on every other scale, plus a rough tensile strength in MPa, ksi, psi, N/mm², or kgf/mm².

Hardness tests use different tips and loads, so the numbers do not match on their own. Shops still need to compare them. A drawing may call for 45 to 50 HRC while your lab report gives HV. This calculator does that swap using the reference values in ASTM E140, the standard hardness conversion tables for metals.

You can convert one value or a whole range, like a min and max on a print. Pick your material type (steel, non-ferrous metal, or plastic) and the tool dims any scale that does not fit that material instead of hiding it. If a value falls outside the table, it says "out of range" rather than guessing.

You also get a step-by-step view of the math, a bar chart showing where your value sits on each scale, and a full lookup table you can sort. Use it for heat treat checks, incoming material checks, quality reports, and reading prints that use a scale your tester does not have.

How to Use Our Hardness Conversion Calculator

Pick a hardness scale, type in your hardness value, and the calculator shows the same hardness on every other scale, plus an estimated tensile strength, a step-by-step solution, a chart, and a reference table.

Mode: Choose Single to convert one hardness value. Choose Range to convert a low and high value at the same time, like a spec range on a drawing.

Quick presets: Tap HRC, HRB, HV, or HB to jump straight to that input scale. This just sets the scale for you and loads a sample value.

Input hardness scale: Pick the scale your test result came from: Vickers (HV), Brinell (HB), Rockwell B (HRB), Rockwell C (HRC), Knoop (HK), Shore A, or Shore D. Tensile strength is an output only, so you cannot enter it.

Material type: Pick Steel/Iron, Non-Ferrous Metals, or Polymers/Elastomers. Scales that do not fit your material are dimmed and labeled, but still shown.

Tensile strength output unit: Choose MPa, N/mm², ksi, psi, or kgf/mm². This changes the tensile numbers in the results, chart, and table.

Hardness value (Single mode): Type your test number, or drag the slider. Stay inside the valid range shown under the box, or you will get an out-of-range message.

Minimum value (Range mode): Enter the low end of your hardness range, or drag the minimum handle.

Maximum value (Range mode): Enter the high end of your hardness range, or drag the maximum handle. The minimum must not be higher than the maximum.

Calculate: Press this button to run the conversion and update every result, or just change any input and the results refresh on their own.

Reset / Clear: Press this to wipe all fields and start a new hardness conversion.

What Is Hardness Conversion?

Hardness tells you how well a material resists being dented. A machine presses a hard tip into the surface with a set force. The size or depth of the dent gives the hardness number. Different tests use different tips and loads, so each test has its own scale. Hardness conversion lets you take a number from one scale and find the matching number on another scale.

The Main Hardness Scales

Vickers (HV) uses a diamond pyramid tip. One smooth scale covers soft metals up to hardened tool steel. Great for thin parts, coatings, and case depth checks.
Brinell (HB / HBW) presses a 10 mm carbide ball with a big load. The dent is large, so it averages out rough grain. Good for castings, forgings, and bar stock.
Rockwell B (HRB) uses a small steel or carbide ball. Used for soft steel, brass, bronze, and aluminum.
Rockwell C (HRC) uses a diamond cone with a 150 kgf load. The most common scale for heat treated steel, dies, bearings, and blades.
Knoop (HK) uses a long, thin diamond tip for very small spots. Used on brittle parts, ceramics, plating, and thin layers.
Shore A and Shore D are spring loaded durometers for rubber and plastic. Shore A fits soft rubber like seals and tires. Shore D fits hard plastic and stiff urethane.

Hardness and Tensile Strength

For plain carbon and alloy steel, hardness and pulling strength move together. A harder steel usually has a higher ultimate tensile strength. That is why a rough tensile value in MPa, ksi, or psi can be read off a hardness number. This link does not work for austenitic stainless steel, aluminum, copper, or plastics.

Why Conversions Are Only Close, Not Exact

Each test loads the metal in a different way, so there is no perfect formula between scales. Conversion charts come from real test data, mostly ASTM E140, and hold best for common carbon and alloy steels. Expect small shifts for cold worked metal, case hardened parts, thin sheet, or odd alloys. Shore numbers overlap the metal scales only at the very top of Shore D, so those matches are rough guides.

Tips for Better Results

Report the scale you actually tested on, then list the converted value as "approximate."
Pick a scale that fits the part. Thin or coated parts need HV or HK, not HRC.
Keep the test surface clean, flat, and backed so the part cannot flex.
Take three or more readings and use the average.
For a part spec, a hardness range such as 45 to 58 HRC is safer than one single number.

Formulas used

Linear interpolation factor between bracketing table rows

t = \frac{H_{\text{in}} - x_0}{x_1 - x_0}

Interpolated value on the target scale

y = y_0 + t\,(y_1 - y_0)

Conversion to the Vickers pivot column

HV = HV_0 + t\,(HV_1 - HV_0)

Tensile strength unit conversion from MPa

\sigma_{\text{unit}} = \frac{\sigma_{\text{MPa}} \times 10^6}{f_{\text{unit}}},\quad f_{\text{MPa}}=10^6,\; f_{\text{ksi}}=6894757,\; f_{\text{psi}}=6894.757,\; f_{\text{kgf/mm}^2}=9806650

Bar chart position within a scale's full range

P = \frac{v - v_{\min}}{v_{\max} - v_{\min}} \times 100\%

Zone-bar sampling point across the valid input range

v_i = v_{\min} + (v_{\max} - v_{\min})\,\frac{i}{N},\quad i = 0,1,\dots,N,\; N = 100

Green-zone threshold for available conversions

\text{thr} = \max\!\left(1,\; \left\lceil 0.75 \cdot c_{\max} \right\rceil \right)

Frequently asked questions

What is 55 HRC in Brinell and Vickers?

55 HRC is about 595 HV and about 560 HB. It also lines up with roughly 1830 MPa (265 ksi) of tensile strength in steel.

These numbers come from the ASTM E140 tables for carbon and alloy steel. Treat them as close matches, not exact swaps.

What is the hardest steel on the Rockwell C scale?

Most published conversion tables stop near 68 HRC, which is about 940 HV. Fully hardened tool steels like M2, D2, and some powder metal grades land in the 60 to 66 HRC range.

Above 68 HRC the Rockwell C test loses meaning because the diamond cone barely moves. Labs switch to Vickers or Knoop for those cases.

Why is there no Rockwell C value for soft steel?

Rockwell C uses a diamond cone with a 150 kgf load. On soft metal the cone sinks in too deep, and the reading is not repeatable.

That is why HRC tables start around 20 HRC (about 240 HV). Below that, use Rockwell B, Brinell, or Vickers instead.

How do I convert HRC to tensile strength?

Convert HRC to Brinell or Vickers first, then use the steel rule of thumb:

Tensile strength (MPa) ≈ 3.45 × HB
Or: Tensile strength (ksi) ≈ 0.50 × HB

Example: 40 HRC ≈ 371 HB, so tensile ≈ 3.45 × 371 ≈ 1280 MPa (about 186 ksi).

This only works for non-austenitic steel. It fails for stainless 304/316, aluminum, copper, and plastics.

What is the difference between HB and HBW?

Both mean Brinell hardness. The W stands for tungsten carbide ball.

Older tests used a hardened steel ball, marked HBS. Steel balls flatten on hard parts, so modern standards (ASTM E10, ISO 6506) require carbide. Today almost every Brinell number you see is really HBW.

What hardness is 45 HRC in HRB?

There is no HRB value for 45 HRC. The two scales barely overlap.

Rockwell B tops out near 100 HRB, which is only about 22 to 24 HRC. Anything harder than that must be read on Rockwell C, Vickers, or Brinell.

Is Shore D the same as Rockwell?

No. Shore D uses a spring loaded cone on rubber and plastic. Rockwell uses a fixed dead weight on metal.

They only touch at the very top of Shore D, around 78 to 100 Shore D, which lines up with roughly 80 to 170 HV. That is still softer than any hardened steel. Never use a Shore number on a metal print.

What hardness should a knife blade be?

Most kitchen and pocket knives run 56 to 62 HRC.

56 to 58 HRC: tougher, easier to sharpen, chips less. Good for choppers and outdoor knives.
59 to 62 HRC: holds an edge longer but is more brittle. Common in Japanese kitchen knives.
Above 63 HRC: very long edge life, but the tip can snap.

How hard is 6061-T6 aluminum?

6061-T6 is about 95 HB or roughly 60 HRB. In Vickers that is close to 100 HV.

Aluminum is far too soft for Rockwell C. Use HRB, Brinell, or Vickers. Also skip the hardness to tensile rule, since it was built for steel.

Which hardness test should I use on thin parts or coatings?

Use Vickers (HV) or Knoop (HK). Both use tiny loads and leave small dents.

A good rule: the part must be at least 10 times thicker than the dent depth. Rockwell C and Brinell make deep, wide dents that push through thin sheet and read the backing plate instead of the part.

Why do two hardness testers give different numbers on the same part?

Common causes:

Rough or dirty surface, or leftover scale and decarb
Part not flat or not supported, so it flexes
Dents placed too close to each other or to an edge
Worn indenter or a tester that is out of calibration
Uneven case depth or coarse grain

Take three or more readings in different spots and average them.

What is case hardening and why does it affect hardness readings?

Case hardening adds carbon or nitrogen to the outside of a steel part. The skin gets hard while the core stays soft and tough.

A deep test like Rockwell C or Brinell can punch through a thin case and read the soft core, giving a low number. For case depth work, cut a cross section and use Vickers or Knoop micro-hardness readings along the depth.

Can you convert hardness for stainless steel the same way as carbon steel?

Not reliably. Standard ASTM E140 tables are built for non-austenitic steel.

Austenitic grades like 304 and 316 work-harden right under the indenter, so scale to scale matches shift and the tensile estimate can be badly off. ASTM E140 has separate tables for austenitic stainless, nickel alloys, and other materials. Always list which scale you actually tested on.

What is the hardness of mild steel?

Hot rolled mild steel like A36 or 1018 runs about 120 to 160 HB, which is roughly 67 to 83 HRB or 125 to 170 HV.

That works out to about 400 to 520 MPa (58 to 75 ksi) tensile strength. Cold drawn 1018 sits higher, near 160 to 180 HB.

What does 45-50 HRC on a drawing mean?

It is a required hardness range after heat treat. The part must test between 45 and 50 on the Rockwell C scale.

A range is used instead of one number because heat treat always varies a little. In Vickers that span is about 450 to 510 HV; in Brinell about 425 to 475 HB.

Rate this calculator