Inch-Pound to Metric Conversions

SpecLink-E mostly uses soft conversions.  Some other types of conversions are defined below.

“Soft” Conversion: A “soft” conversion is “rounding an exact conversion within the tolerances of the original value”.

  • Example: 4-1/8 inches (4.125 inches) converts to 104.7750 mm; to four significant figures, that result becomes 104.8 mm. The difference between the exact conversion and the rounded one is less than the original 1/8 inch tolerance.
  • The overwhelming majority of SpecLink uses of metric conversion will be of this type.

Exact Conversion: One dimension multiplied by the appropriate conversion factor and the result given with the appropriate number of significant digits.

Hard” Conversion: A “hard” conversion is “conversion to a new and non-interchangeable value based on preferred or convenient numbers and involves a change in size or physical properties”. EXAMPLE: A four inch linear measurement soft converts to 101.6 mm. A four inch linear measurement hard converts to 100 mm. This type of conversion is usually tied to a specific product or application, like a European tile which is 300 mm by 300 mm (which soft converts to 11.8 inches by 11.8 inches), but is marketed and sold as “12 inch by 12 inch (nominal)”.

  • ALWAYS: Verify that hard conversion is appropriate to a specific case before using it.