Adding Seam Allowances

One of you emailed me with a question that got me thinking: how do you add seam allowances?  I wonder if it’s one of those things so simple that everyone assumes they know how everybody else does it.  I hope some of this looks familiar!

Method 1 With a Sewing Gauge

Adjust slider to the desired SA and place along the stitching line.  Draw little lines against the edge of the gauge.  Repeat at regular intervals and join with a ruler.

For curved areas, draw smaller lines at shorter intervals.  To join up, I go freehand: a good method if you haven’t a fashion curve (or prefer not to use one).  Turn the pattern so the line curves in towards you (i.e. not away from you) and with your elbow pivoting on the table and your hand still, turn your forearm in a smooth arc with the pencil skimming along the little lines.

Method 2
Using a Fashion Curve

Align the desired seam allowance with the stitching line and draw along edge.

As before, on curves such as the armscye, keep realigning and mark lines a little and often.


So far so simple.  But there’s more…


3 How to Add Seam Allowances to Darts

Draw seam allowances up to the dart (on both sides).  Pin dart closed, folded in the direction you want it pressed on the garment.  The seam allowances and stitching lines should now meet. Cut along the seam allowances.

Remove pin and the pattern looks like this:

Try not to skip this step or you may have a shortage of fabric in your dart when you come to sew the seam.

4 Adding Seam Allowances to Angles

When two stitching lines meet at a right angle, no problem: the SAs are also right angles.  It gets trickier when the angles are sharp, large or curves, for example in the neck to shoulder corner, or waist to side.  If you serge your seams, what follows is perhaps less of a concern.  If you press seams open or don’t trim the allowances much (for example, if you might need to let out a garment later), you may want to add the following to your method:

Step 1 Draw the Seam Allowances up to the corners but don’t cut.

Step 2 Fold the pattern back along the stitching line then cut along the seam allowance on fold.

Do this on all curves and angles that are not L-shaped: i.e. fold back at stitch line, cut on fold along seam allowance edge.

The opened up piece will have pointy bits like this:

When the seam allowance is pressed open after stitching, there is enough fabric to align with the fabric of the cross seam.


So, any revelations?  Did I miss any tricks?! How do you add yours?