How to Sew a French Seam

What is a French Seam?

This is a seam that encloses the raw edges of your fabric so that they are no longer visible. As a result there is no need to finish your seam with a zig zag stitch or an overlocker.

Why use a French Seam?

Because the raw edges are enclosed they create a neat and tidy finish to the inside of your garment. This is particularly handy when you have seams that will be exposed e.g. on an unlined jacket. This is why I used a French seam when sewing a cropped evening jacket, see Pattern Review of Butterick 5529 .

They are commonly used when sewing with sheers as the seam blends with the fabric. They are significantly less obvious than overlocked or zig zag seams.

Additionally, they are incredibly strong which is good when you are making clothes that will be going through the wash a lot. Also, they may feel softer against your skin than an overlocked or zig-zagged seam.

When should I use a French seam?

They work well on light and medium weight fabric but not so well on heavy weight fabric as the seam will be really bulky. They are most commonly used on straight seams but can be used on curved seams if a very narrow SA is used.

How to sew a French seam:

Before you start:

One thing to note before you start is that you are splitting your SA into two parts, as you are sewing two rows of stitches for each seam. This tutorial is for a 1.5 cm SA. However, the instructions below can be adapted if you want to increase or decrease the SA. For example, you may find it easier to sew a wider seam allowance for the first step and trim it down.

Accuracy is really important as you are sewing twice for each seam, so if each step is a little off you could massively affect the way the garment fits. If you are sewing 2 French seams and are a ¼” off in each step, it will add up to a 1” difference in the overall fit!

Furthermore,  have an iron ready as French seams involve a lot of pressing to ensure you get a good finish.

Let’s get sewing:

  1. Pin the seam WST. Sew using a 1cm seam allowance. Backtack at each end.
    • For this step you are sewing a seam as you would normally only with the WST.
Sew a french seam
Sew WST with a 1 cm SA.
2. Press the seam open.
sew a french seam
Press the seam open.

3. Trim the SA to 3 mm.

4. Fold the fabric RST along the stitching line.

5. Press along the fold. You want to have a sharp crease at the fold of the first seam.

6. Pin the seam RST to enclose the raw edges.

sew a french seam
Pin the seam RST

7. Sew the seam RST with a 0.5 cm SA. Back tack each end. The raw edges should now be enclosed. Make sure that the SA from the first seam is not sticking out.

sew a french seam

8. Press the seam.

sew a french seam

If you have a fabric that is fraying as you sew make sure you tuck the threads into the seam or trim them as you go. You don’t want threads sticking out of your finished seam. Do not pull them as it will make the fraying worse