Sewing · Tutorial
French seams without fuss
A French seam encases the raw edges inside the seam itself, so a bread cloth or a lightweight curtain has no fraying inside and no serger required. It looks like a professional finish because it is one, and it takes two straight lines of stitching.
Step by step
Step 1
Know your seam allowance maths
A French seam uses your full allowance in two passes. With a standard 5/8 inch allowance: sew the first pass at 3/8 inch, trim to 1/8, then sew the second at 1/4. The two passes together equal your original 5/8, so the finished garment stays true to size.
Step 2
Start wrong sides together — yes, really
Pin the pieces with wrong sides together, raw edges matched. This feels backwards. It is the whole point: the first seam is sewn on the outside so it can be folded inside.
Step 3
Sew the first pass at 3/8 inch
Straight stitch, 2.5 mm, no backstitch flourish at the ends — just a few securing stitches. Keep the line even; a wobble here shows through the finished seam.
Step 4
Trim hard, to a scant 1/8 inch
Trim the allowance down close and evenly. This is the step people skip, and it is the reason their French seams look lumpy. Anything left behind will try to poke out of the finished channel.
Step 5
Press the seam open, then closed
Press the seam open flat first, then fold right sides together along the stitch line and press again so the seam sits exactly on the fold. Roll the fold between your fingers to get the stitching right to the edge before you press.
Step 6
Sew the second pass at 1/4 inch
With right sides now together, stitch 1/4 inch from the folded edge. That line must clear the trimmed edges inside — if a whisker of raw edge escapes, your trim was too generous or your fold rolled.
Step 7
Press the finished seam to one side
Press the encased seam toward the back of the garment, or toward the hem on flat goods. Topstitch it down if the cloth is soft and wants to flop.
If it goes sideways
Whiskers of raw edge poking through means the trim was not close enough — unpick the second pass, trim again, redo it. Puckering means the cloth was fed under tension or the stitch length is too short for a fine weave; lengthen to 2.5–3 mm and let the feed dogs pull. And French seams do not belong on curves tighter than a gentle armhole, or on heavy cloth — use a flat-felled seam there instead.
The Mercantile Letter
Notes from the workroom
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