It could be as big as you want it to be, but it is usually about a half and inch wide all the way around. The standard seam allowance is 5/8 inch.
so that the material does not fray.
The fabric between the seam and the cut edge is referred to as the seam allowance.
The seam is simply the name of the line that is created when two pieces of fabric are joined together. If you are sewing any two pieces together, the place where they are joined is called the seam. Maybe you are wondering about the seam allowance, which is the amount of fabric alloted to sewing the pieces together. The seam allowance is the distance from the edge you put your line of sewing. In many fabrics that allowance can be very small, but some fabrics require a larger allowance to minimize fraying.
A seam with no seam allowance. Right sides are the same side up and you you zig zig stitch the pieces together with or without an underlay.
sew a seam with a 5/8 seam allowance. then on ONE SIDE of the allowance, trim it to half the size. don't measure just eyeball it. then press the seam allowance to one side with the [now] short allowance on top. fold the longer allowance over the shorter and press it. then flip the whole thing to the other side of the seam and press again. finally, topstitch as close to the edge as you can. flat felled seams are the strongest and are used where ever a great amount of tension exists, such as the seams on your jeans, or the shoulders in a shirt/jacket. they are also used in sports clothes.
the standard is 5/8
These measurement grooves are a seam gauge. They measure how big your seam allowance will be. As you sew, you'll align the edge of your fabric with one of the grooves. The grooves are labeled with "3/8", "4/8", "5/8", etc. If you line the edge of your fabric up with the 5/8 groove as you sew, you will have a 5/8" seam allowance, and so on.
When sewing, you'll want to leave a sewing margin (or a "seam allowance") for a couple of reasons:A 5/8" margin (the standard seam allowance) between the stitch and the edge allows for a little reinforcement, and places less stress on the stitch. This will keep the stitch from breaking easily.A margin allows you to later let out the seam, in case you need more room (for example, if a skirt gets too tight, you can loosen it if there's seam allowance).
Anybody answer this question......
The seam allowance is needed to allow for extra fabric where separate pieces of fabric are joined together at seams. If seam allowances were not provided you wouldn't be able to join pieces together or your garment would end up being too small. If you look at the inside of a shirt, for example, you will see that the stitches take up fabric and that is what seam allowances are for.
Inner curves need to be clipped so that the seam allowance can spread and lie flat once the item is turned.