A French seam encloses the raw edges inside the seam itself, so the inside of the garment is as clean as the outside. It is sewn twice, and the order feels backwards the first time.
The method, from a 15 mm seam allowance.
One. Place the pieces wrong sides together and sew 7 mm from the edge.
Two. Trim that seam allowance down to about 3 mm. Trim it evenly — anything left long will poke out of the finished seam as whiskers.
Three. Press the seam open, then fold the fabric so the pieces are now right sides together with the seam exactly on the fold. Press again. This press is what keeps the finished seam narrow.
Four. Sew 8 mm from that fold, which encloses the trimmed edges completely.
Five. Press the finished seam to one side.
Where it belongs. Sheer fabric, where any seam finish would show through. Unlined garments in fine fabric. Silk and cotton lawn, which fray badly. Children’s clothing, where a soft enclosed seam is comfortable.
Where it does not. Curved seams — the enclosed allowance cannot spread, so a French seam on an armhole distorts. Thick fabric, where the double allowance is bulky. And anywhere you will need to let the seam out later.
The usual mistake is sewing right sides together first out of habit. Check before you sew; unpicking step one is tedious.
Questions people actually ask
Can I French seam a curve?
A very gentle one, with the second seam sewn slowly. On an armhole or a tight curve use a bound or overlocked seam instead.
My seam has whiskers poking out.
The first allowance was not trimmed evenly, or the second seam was too narrow. Trim to a consistent 3 mm and sew the second seam a little wider.
Last reviewed 2026-08-11