Hardness Converter and Conversion Chart — Rockwell A to K, Superficial Rockwell, Brinell, Vickers, Shore Scleroscope and Tensile Strength

Convert Between Every Common Hardness Scale

Type a hardness on any scale and read it on every other one: Rockwell A, B, C, D, E, F, G, H and K, superficial Rockwell 15-N, 30-N, 45-N, 15-T, 30-T, 45-T and 15-W, Vickers, Knoop, Brinell, Leeb (type D), Shore scleroscope, and the approximate tensile strength of carbon and low alloy steel. Separate tables cover steel, nickel alloys, cartridge brass, austenitic stainless steel, copper, white iron and wrought aluminum, because a conversion is only valid for the material it was measured on. Below the calculator is the full conversion chart, which you can print as a poster in any paper size.

The numbers are exactly as printed in ASTM E140, the standard hardness conversion tables, and in the USAF/Navy manual TO 1-1A-9. The two sources were checked against each other and against published charts (card 06). Between printed rows the calculator interpolates in a straight line, and it never goes past the ends of a table. Hover over the i next to any scale to see how that test is made and what it is used for.

Hardness Conversion
Material
Hardness You Measured
Equivalent Hardness
Values marked ≈ are interpolated between two printed rows. Blank cells in the source table are skipped, so the two rows used may be more than one row apart.
Not Converted
HARDNESS CONVERSION CHART
read across a row · TO 1-1A-9
Your calculator value is the highlighted row. Click a row to load it into the calculator.
Reference Guide — Hardness Tests and Conversions
01

How to Read the Chart

Each row is one hardness level. Read across the row to compare the scales: in the E140 steel chart, HRC 40 sits on the same row as HV 392, HB 371, HK 402, HRA 70.4 and HR30N 59.5. The shaded first column is the chart's key scale. Under each scale name the heading gives the indenter and the load. A value in parentheses is outside the range the standard recommends for that test.

A dash means TO 1-1A-9 prints nothing there: that scale is not used at that hardness. Several superficial and ball scales are printed only on every other row. The calculator interpolates across those gaps, and the chart shows only the printed values.

Pick the chart for your material
  • ASTM E140: non-austenitic (carbon, alloy and tool) steel in the C and B ranges, nickel and high-nickel alloys, cartridge brass, austenitic stainless plate and sheet, copper, alloyed white iron and wrought aluminum.
  • TO 1-1A-9: hardened steel and hard alloys (to HRC 80, with Rockwell G), soft metals with the E, G, H and K ball scales and Brinell at 500 kg, and approximate tensile strength of carbon and low alloy steels.
Conversions are approximate. TO 1-1A-9 para 8.1: when a drawing or specification names a hardness test, make the reading with that test whenever possible rather than converting from another one.
02

How Each Test Is Measured, and What It Is Used For

Sources are given in each row. TO 1-1A-9 paragraph 8.2 lists the methods in general use as Brinell, Rockwell, Vickers, Tukon (a Knoop microhardness tester) and Shore scleroscope.

03

Every Rockwell Scale and What It Is Used For

A Rockwell number means nothing without its scale letter, which names the indenter and the load (TO 1-1A-9 para 8.3.1). Every Rockwell test first seats the indenter with a 10 kg minor load, then applies the major load below. The diamond scales read on the black dial figures and the ball scales on the red ones.

Choosing a scale (TO 1-1A-9 para 8.3.1.1). Start with the diamond if you are unsure. Below about C20 (B98) the material is too soft for the diamond: change to the 1/16″ ball or a larger one. Above B100 use the diamond, because the ball may be deformed. Larger balls (1/8, 1/4 and 1/2″) are for soft metals, and the ball is chosen for the hardness range of the material.

Rockwell E uses a 1/8″ ball at 100 kg. ASTM E18 (via NIST SP 960-5) lists it for cast iron, aluminum and magnesium alloys, and bearing metals. The E140 wrought aluminum table and the TO 1-1A-9 soft-metal tables both give E-scale conversions.

Rockwell C and B are the most commonly used scales (TO 1-1A-9 Table 8-4). E18 also notes an upper limit of G92 on the G scale, to avoid possible flattening of the ball.

How the dial number comes from depth (NIST SP 960-5): with the diamond, regular Rockwell = 100 − h/0.002 mm and superficial = 100 − h/0.001 mm; with a ball, regular Rockwell = 130 − h/0.002 mm and superficial = 100 − h/0.001 mm, where h is the extra depth under the total force after it is removed back to the preliminary force.

NIST SP 960-5 Table 1 (from ASTM E18). Preliminary force 10 kgf for the regular scales and 3 kgf for the superficial scales.

04

Hardness and Tensile Strength

When a drawing specifies tensile strength but a tension test is impractical, TO 1-1A-9 (para 2.8.2) allows hardness tests using the equivalent hardness in Table 8-5. The relationship is approximate and is a guide only (para 2.8.3):

  • It applies only to plain carbon and low alloy steels, not to corrosion-resistant, magnet, valve or tool steels.
  • It should not be used for non-ferrous alloys (para 8.1).
  • Where a narrow range of hardness is required, establish the hardness-strength relationship by tests on the actual part.
  • Hardness values should be within two points Rockwell, or 20 points Brinell or Vickers.
  • The relationship is uniform for parts large and rigid enough to take a full indentation on a flat surface without deflecting. Small cylindrical parts read lower on Rockwell than the table shows for their tensile strength.
  • Buffing, plating, decarburized or porous areas and hard spots all change the relationship: grind those surfaces away before testing.

The calculator reads tensile strength from Table 8-5 at the same Rockwell C value (or Rockwell B, for the soft-metal chart). It shows tensile strength in ksi (1000 psi, as printed) and in MPa (1 ksi = 6.894757 MPa).

05

Getting a Good Reading

  • Remove cladding, decarburized layers, scale, oxide, pits and anything else that could affect the reading (TO 1-1A-9 paras 8.1, 8.3.2).
  • Test on a single thickness, flat, with nothing bulging on the side opposite the indentation. Keep Rockwell tests at least 1/8″ from the edge.
  • On a curved part put the concave side toward the indenter, and support any overhang.
  • Take several readings (3 to 6 is usually enough) at different points and average them (para 8.3.2.1).
  • Check a Rockwell tester regularly on test blocks; recalibrate if it is more than ±2 hardness numbers out (para 8.3.2.2).
  • Brinell: do not indent a curved surface of radius under 1″, keep the load square to the surface within 2°, and apply it steadily (AC 43.13-1B para 4-18).
  • Every hardness test leaves a small pit. Do not test sealing surfaces, fatigue-critical parts or load-bearing areas of parts going back into service (AC 43.13-1B para 4-16).
  • For aluminium alloys, hardness tests are useful mainly to tell annealed, cold-worked, heat-treated and aged material apart (AC 43.13-1B paras 4-16, 4-23).
06

Source Check: How Well the Charts Agree

Every value in TO 1-1A-9 was compared with ASTM E140 at each Rockwell number both print. The table below is computed on this page from the two data sets. The Rockwell and superficial scales agree to within TO 1-1A-9's 0.5-point rounding. Vickers and Brinell agree within a few percent; the largest gaps are at the very hard end, where E140 prints its carbide-ball Brinell values in parentheses as outside the recommended range.

Against published charts

The Leeb table agrees with the ASTM E140 block of Proceq's steel conversion chart at every point checked (card 07). Spot checks at HRC 50, 40, 30 and 20 against two widely used charts:

  • Benedict-Miller (SAE data for carbon and alloy steels): Brinell, Vickers, Rockwell A and 30-N identical to E140 Table 1 at every check point; tensile strength within 3 ksi of TO 1-1A-9 Table 8-5.
  • West Yorkshire Steel (UK): Vickers within 1 % and Brinell within 4 % of E140 at HRC 40, 30 and 20. At HRC 50 its Vickers (547) is higher than both E140 and TO 1-1A-9 (513).
Why charts differ. ASTM E140 (para 1.12, section 6): conversions are only approximate, are valid only for the material they were measured on, and can be affected by alloy, grain structure and heat treatment. Differences within one scale can be larger than between two scales or instruments. Convert only when the specified test cannot be made.

The printing problems found in TO 1-1A-9 are listed in card 07.

07

Sources

  • ASTM E140-02, Standard Hardness Conversion Tables for Metals, Tables 1 to 9: non-austenitic steels (Rockwell C and B ranges), nickel and high-nickel alloys, cartridge brass, austenitic stainless steel plate and sheet, copper, alloyed white irons and wrought aluminum products. Values transcribed by a script that reads the PDF and checks every column. Values printed in parentheses are shown in parentheses.
  • ASTM E140-12b Table 10, Leeb (type D) hardness conversion for non-austenitic steels, Rockwell C range. Transcribed from a reproduction published by UTS Canada that cites E140-12b, and checked against the “According to ASTM E140” block of Proceq's Hardness Conversion Chart for Steel & Cast Steel (HLD 809 = HRC 60 = HV 711; HLD 600 = HRC 34.5, HV 335; HLD 510 = HRC 20 = HV 234 = HB 229).
  • NIST SP 960-5 (2003), S. R. Low, Rockwell Hardness Measurement of Metallic Materials, Table 1: Rockwell scales, forces and typical applications (as given in ASTM E18), and the depth formulas. Cross-checked with ASTM E18-15 Table 1.
  • TO 1-1A-9 / NAVAIR 01-1A-9, Technical Manual, Engineering Series for Aircraft Repair: Aerospace Metals — General Data and Usage Factors, 17 October 2025. Chapter 8 (Tables 8-1 to 8-5, paras 8.1 to 8.6) and paras 2.8.1 to 2.8.3. Distribution Statement A: approved for public release, distribution unlimited. Transcribed by a script that reads the PDF and checks that each column falls monotonically down its table. Tensile strength on this page comes from its Table 8-5.
  • FAA AC 43.13-1B, Acceptable Methods, Techniques, and Practices — Aircraft Inspection and Repair, paras 4-16 to 4-21 and 4-23 (hardness testing, Brinell, Rockwell, Vickers, microhardness and Knoop).
  • ASTM E384, Microindentation Hardness of Materials (scope: Knoop and Vickers, 1 to 1000 gf). ASTM D2240, Rubber Property — Durometer Hardness (scope and significance). ASTM A956, Leeb Hardness Testing of Steel Products (scope). Cited for what each test is; no values are taken from them.
  • Published charts used only for the spot check in card 06: Benedict-Miller, Hardness Conversions; West Yorkshire Steel, Hardness Conversion Chart.
  • Printed values kept as printed. Table 8-5 prints Rockwell B 130.7 at C27, between 104.3 (C28) and 102.9 (C26); the chart shows it underlined and the calculator does not use it. Table 8-5's Brinell heading reads "300 Kilogram Load" and carries a footnote mark (3) with no footnote text. Table 8-1's 30-N column is headed "50-N" with a 30 kg load.

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