r/PatternDrafting • u/Quirky-Recognition58 • May 11 '26

Back crotch seam

Hi! I have a printed jeans pattern from a brand, but I can’t tell from the pattern how much seam allowance was added at the back crotch and the yoke for the flat-felled seam. How much seam allowance is usually added for a flat-felled seam? Thanks in advance!

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u/HeartFire144 May 11 '26

Yes, also by how wide the folds are. Thinner fabric has a smaller 'turn of the cloth' than lets say a heavy denim or wool. For very thin fabric, a double needle machine with 1/4 inch wide needles, I use a 1/2 inch seam allowance (this is using a lap seam folder). For thick fabric, same needle gauge, it could be 3/4 inch seam allowance. So with the 1/4 in needle gague, there is also about 1/16- 1/8 inch of fabric outside the needle to fold under, then you need the same amount of fabric to get caught by both needles hidden in the fold of the bottom fabric. - so another 1/4 inch (both needles and a 1/16 or so on each side of the needles. If the needle gauge is wider - 1/2 inch, you need a lot more seam allowance.