Shaping Seam Allowance for Corners and Curves

Shaping Seam Allowance for Corners and Curves


Hermès, AW11, Paris.

Constructing a garment is a complex process which goes back and forth between cutting the fabric and stitching the fabric, more cutting, more stitching, more pressing until eventually you get the fabric to sit the way you want, engineered into the desired shape.

One of the most fundamental steps in making seams sit the way you want is in the way that you deal with the seam allowance, i.e. the small border of extra fabric that ends up inside the garment.

Many a perfectly good student garment has been ruined because the student has not been ruthless enough when dealing with seam allowance, leaving their garments looking bulky and unresolved. This is because if seam allowances are not engineered correctly then they will only end up getting in the way and the seams will be hard to press flat.

Corners and curves are situations which especially require careful consideration than straight seamlines. The images below depict sections of Hermès garments where seam allowance needs to be correctly trimmed and shaped – otherwise it would ruin the whole flow of the design lines of the garment.


Seam allowance becomes especially difficult once you start reaching complex junctions of many seams, but the diagrams below will depict the basic ways of dealing with seam allowance. More complex situations will become a combination of these techniques, and of others, but these diagrams below outline the fundamental ideas.

Basic description of how to read the diagrams below:image

And a few points to remember before you start trimming:

  • In most cases with corners you will not get the right result unless you cut right up to within a few threads of the stitching line.
  • Note that you should not cut too close to the stitching line or else you will not have enough fabric left for the stitching to hold together.
  • You can always cut into your fabric by small amounts first to test what you are doing, press and then if need be, turn the fabric round and trim or cut in a little bit more.
  • You should trim and cut as you are building your garment for best results, not just leave it all for the end. At some stages of your garment it will be easier to press the corners and curves, and if you sew too far past this stage sometimes these sections will become harder to access.
  • There are other techniques for dealing with seam allowances which we will explore in later posts. So if these fundamentals don’t work for your fabric then experiment with your own ways of making it work, based on these principles.

Seam Allowance Trimming an Outward Corner:

This is for situations such as collar points, cornered lapels, angular shapes etc. If you sew a corner and then do not trim any excess fabric away then your corner will never look sharp, as there will be too much bulk in there. Basically when you turn the seam around the right way, the fabric has nowhere to go and just bunches up on itself in the corner. When the excess is trimmed away, the seam allowances will be able to sit inside the garment as in Image 4 below, with the seam allowance fitting neatly into the space inside the garment.


Seam Allowance Trimming for Inward Corners:

This can occur in shaped lapels, or sometimes on geometric necklines. This time you do not need to cut anything away, you just need to create a small slit, so that once the garment is turned the right way round the split will allow the two edges to swing away from each other. If you leave this uncut, there will be tension in the corner of the garment, as the two edges will want to pull away from each other but won’t be able to.


Seam Allowance Trimming for Outward Curves:

This works on the same principle as the outward corner, in that you need to make space for the seam allowance on the inside of the garment once the seam is turned the right way round. But this time instead of the excess needing to be removed from just one place, the space needs to be spread evenly around the curve. As a learning experiment you could sew two curved seams exactly the same. Cut the first with small triangles quite close together, and for the other cut much fewer triangles which are wider. You will find that the smaller, evenly spaced triangles will enable you to have a smoother curve once the garment is turned the right way round. The sparser, wider triangles are more likely to give you something edging closer to the shape of a hexagon, rather than a nice smooth curve.


Seam Allowance Trimming for Inward Curves:

Again this is similar to the inward corner in that you are simply splitting the fabric, rather than cutting excess away. It is also similar to the outward facing curve, in that you will get a better result if you cut slits more often, as this will release tension evenly around the curve.


Catwalk images from»

Images of seam allowance by The Cutting Class.

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