Steel Hardness Converter

Convert from any scale. Choose any scale in the active table under “Convert from” and enter a value; the tool locates the matching table row on that scale and reads across the rest. Because A370 tables are keyed on Rockwell C and B, entering on another scale finds the Rockwell row(s) whose listed value matches yours.

Values between table rows — conservative step-down. A370's tables are discrete. When a reading falls between two printed rows, this tool resolves it to the row representing the lower hardness — never the higher one — and reads that single row across. Converting upward would credit the material with hardness it has not demonstrated, so the step is always taken in the conservative direction for acceptance work. Example: a Knoop reading of 825 HK falls between the listed 822 (64 HRC) and 846 (65 HRC); it resolves to 822, giving 64 HRC. A reading that lands exactly on a printed value is used as-is with no adjustment.

Direction on inverted scales. Lower hardness is not always the lower number. On Brinell indentation diameter (Table 5) a larger diameter means softer material, so the conservative step there is toward the larger diameter. The tool accounts for this; the input cell always shows the value actually used alongside the value you entered.

Output rounding — ASTM E29-22. The step-down above selects the table row; it is not a rounding operation. Rounding is applied to the reported results using the rounding method of ASTM E29-22 Section 7.4, including the half-to-even convention of 7.4.3: the digit in the last retained place is increased only if it is odd, so a value of 45.5 reports as 46 while 46.5 reports as 46. Results are given to each scale's normal unit — whole numbers for Rockwell C/B, Vickers, Brinell, Knoop and tensile, one decimal for Rockwell A and the superficial scales — which also satisfies A370 16.1, requiring converted Rockwell and Vickers numbers to be rounded to the nearest whole number. Some scales (Brinell, tensile) are blank over part of the range in A370; a blank cell means the standard lists no value there.

Which table applies. Nonaustenitic steels use Tables 2 (Rockwell C basis) and 3 (Rockwell B basis); austenitic steels use Tables 4 and 5. The nonaustenitic tables have been shown applicable to ferritic and martensitic stainless but must not be used for austenitic stainless.

• All converted numbers are approximate. Converted Rockwell and Vickers numbers round to the nearest whole number. Apply with care.
• Tensile strength is approximate and is not provided for austenitic steels; it must not be used for hard-drawn wire.
• Fixed-location report format: state the measured scale, e.g. 353 HBW (38 HRC) — a 38 HRC reading converted to Brinell 353.

Portable hardness testing — A370 Section 19 reporting. Portable results carry a method designation; converted values append the portable instrument in parentheses:

Per A370, converting portable numbers through these tables may carry a larger approximation range than converting fixed-location numbers. Where precise conversions are required, develop them specifically for the steel composition, heat treatment, and part.