Why does the seam allowance shrink as it approaches the top of the slit?

To keep the look of two straight lines meeting each other at a point, both stitch lines must appear straight, not curved or bent at a sharp angle. Take a look at the first diagram below. It represents a slit in a piece of fabric:

Diagram of slit fabric

If you try to stitch around the slit exactly 1/2″ (or 5/8″) away from it, here are examples of what you might get:

Different ways to stitch around the top of a slit

On the outside, gores stitched these ways would look like this, respectively:

Shapes of gore tops

If you stitch around the slit as seen below, you will get the appearance of two straight lines meeting in a point on the front of the fabric:

Straight stitches meet at a point

This is why your seam allowance is tiny at the beginning of the slit and large at the end.


  1. Gillian Wallace says

    Thank you! This is very helpful for inserting flared gussets into tops as well.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: