Don’t feel bad. These terms are often misused in the push to convert the construction industry to metrics. The confusion stems from an illogical switch of terms. Logic suggests that a “hard” conversion would be an exact conversion, while a “soft” conversion would be approximate. NOT SO! The opposite is true. So these are the definitions we must live by:
Soft metric conversion – this is an exact or nearly exact conversion of U.S. Customary (inch-pounds) measurements to the metric equivalent by multiplying by a metric conversion factor and rounding to a practical level of precision. This means the physical dimensions of a product remain unchanged. A good example is batch plant literature that shows inch-pound measurements with metric equivalents in parentheses.
Hard metric conversion – after a soft metric conversion, a similar but rounded rationalized metric number that’s convenient to work with and remember, or where appropriate, to fit the product into an internationally recognized modular product, is used. This means the physical dimensions of a product are changed. Often times hard conversion is preferred to get rid of the undesirable odd metric values of soft conversion. Examples of hard conversion are brick, concrete block, plywood and other building products.
CPMB, in its metric standards, has used hard conversion to establish metric equivalents. It’s not an exact conversion, but it agrees with international ratings and standards.
