The Upholstery Forum

I'm wondering why the standard for patterns and actually sewing up pieces are 1/2 inch. at some points in my projects I want to try to sew at a 1/4 for my curves and a 1/2 for my straights, also the same for my patterns. But I keep my curious thinking no a minimum because I know the standard is 1/2. So, my question is can someone explain why?

No idea why 1/2" is the standard. Although it works fine even on curves. You will however need to make some relief cuts in order for the material to take a curve sometimes. I don't see how a !/4" seam allowance would change that.

I would think it would be better to keep the allowance the same for the entire part.

I find it that sewing with a 3/8 with 1/2 extra on material contours my curves phenomenally and on my straight aways i use 1\2 to attach velcros hog rings etc. generally was wandering i like to know all the rules so i know how to break the rules with some kind of finesse. Thanks for the info.

For upholstery 1/2" works well for most seams and if you decide to topstitch a seam you have plenty of material in the SA to easily make a felled seam. For material that frays 1/2 enables the stitching not to pull through. For garment construction smaller SA works so as not to bulk up the seams, but even for your jeans where a 5 thread overlocker is used you will see the seam is likely 1/2". 1/2" is not a "standard" but it works well enough.

I was just going to type in what Malcom just said, sometimes I like to move the topstitch out from the seam a bit, 1/2” seam allowance gives me that extra bit you sometimes need

1/2" makes for easy math, and the wider the top-stitch is apart the sloppier it can be and still look good, with less seem allowance your skill has to increase.
1/2" is also good for fabrics that tend to fray easily.
I typically use 1/2" for furniture and 3/8", 5/16" or 1/4" for automotive depending on the bulk, but I have gone down to 1/16" on Shift gators. They look better and flex more with less seam allowance.

Also for patterning foam:
Typically you want to have a 1/2" more foam all the way around to put the cover under tension, but if the foam is really dense then you may only be able to have a 1/4" more foam than the cover.
So people usually cut the upholster the same as the foam and then sew at 1/2" seam allowance to get the 1/2" of compression on the foam from the cover.