In the business of manufacturing clothing, we call making patterns for different sizes “grading.” When we grade a pattern to both smaller and larger sizes, someone determines the grading rules, or how much a pattern piece area increases or decreases. Theoretically, one could grade a pattern to any increase or decrease one wanted, but practically, tradition, human morphology, statistical measurements taken from a significant sample population, and changes in the overall population have necessitated standard sizes. In men's pants this would be a two inch “grade” per size, using the waist measurement as the size designation, starting with an even number (again, arbitrary but traditional).

Another way to look at grading and manufacturing pants is what is the most efficient way to construct pants? Should a manufacturer take the time to draft a pattern for every waist size on the human waist spectrum (theoretically no limit to the number of sizes), or decide more efficiently to draft a pattern every two inches, starting at 26″ up to 48″, that is eleven sizes, of which 32 to 40 represent most of the retail sales? Of course it is much more efficient and profitable to manufacture a limited, but representative, group of sizes.

A final way to view sizing or grading patterns is how small an increase in your pattern piece is practical. A one inch difference between sizes translates to a 1/4″ change at the side seam, and a two inch grade is 1/2″ change. That 1/4″ change can end up being way off specification in the final garment since sewing a seam can be off 1/8″ during production. Better to grade garments with larger differences between them, so they will conform the their original, intended final measurements and intended fit.