As ever, responses to the quiz were very interesting with a lot of good discussion. However, only one party (moi) attempted to answer the posed question because everyone else was derailed (including moi) with the specifics of circumference grades. That is not a criticism. I tell you, I learn more in comments and I’ll bet you do too.
For most targeted manufacturers like you, the optimal size range is two sizes up and down from the middle (base) size making for a total of five sizes. This is because the grade can become diluted unless you’re a whiz-bang gen-you-win expert and have a lot more experience. If a medium were my base size, the size range would be XS, S, M, L and XL.
My mention of SML inspired these comments:
Sarah: I always thought that sizes designated SML etc. bridged 2 sizes. M being an 8-10 and so forth. I know part of the answer; but I want to hear yours.
Esther: Not to side track things too far, but if the sizes in S-M-L span two sizes, do you lean toward the larger of the two or average?
Sarah is correct that S-M-L is more generous in that it covers two sizes or sometimes only one and a half. The SML grade is used for less fitted apparel, it is casual and more generous but it remains its own fitting profile with its own set of grade rules.
The silhouette and fit of numbered sizes is more tightly controlled. In those, the profile customer vs styling matters more. If I were making a princess seamed lined coat and 10 were my block size, my numbered sizes would run 6, 8, 10, 12, 14 (total five sizes). This is not in stone writ but subject to modification once sales came in. If sales were slanted toward the upper end, I’d switch gears to use the 12 for my base size (instead of the 10), drop the 6 and add a 16. If there were more sales in the smaller sizes, I’d make the 8 my median size, drop the 14 and add a size 4. Rinse, lather and repeat but your mileage may vary.
If you’re not sure why I’d limit my range to only five sizes, my company is tiny and I can only do so much -and maybe I know too much, like how much trouble you can get into managing a large size spread. Most women’s wear manufacturers in the US (68%) are tiny companies with fewer than 20 employees who don’t have the resources to cover a larger sizing spectrum. It’s only after a company grows larger that they can add more sizes. Even so, there’s quite a few medium sized firms who only cut the limited size range we’re discussing here. It really depends on the customer attracted to your product line.
If your company is more experienced and has the resources to vett a larger size range, the maximum number of sizes I think are possible before there should be an adjustment for a new shape (size break) are three sizes off to either end. Examples are XXS XS S M L XL and XXL. In my opinion, it tops out there. In numbered sizes, it would be 4, 6, 8, 10, 12, 14, 16 or any combination there of.
Next up, I have an entry that explains the difficulty of managing a larger size spread. This is a concern for even sophisticated and well established firms. It is also a pop quiz.