Split the alteration across both side seams and taper it into the existing seam line. Taking it all out of one side twists the garment.
The method.
One. Put the garment on inside out and pin out the excess along one side seam, in front of a mirror or with help. Measure the total amount pinned.
Two. Halve it. If you pinned out 40 mm in total, that is 20 mm per side seam — and 10 mm added to the seam allowance on each side of each seam.
Three. Mark the new seam line with chalk on both side seams, tapering smoothly into the original line above and below the altered section. An abrupt step shows in wear; the taper should run over at least 10 to 15 cm.
Four. Baste the new seams and try the garment on the right way out before cutting anything.
Five. Sew, then unpick the original seam through the altered section, press, and only then trim the surplus allowance.
Practical points. Unpick and re-sew any waistband, hem or cuff that crosses the seam, rather than sewing over them. Match the original stitch length and thread. And on a garment with pockets in the side seams, this alteration is significantly more work — check before starting.
Where the excess is not at the sides, taking in the side seams is the wrong fix. Width across the back, gaping at the neck and a loose bust each need their own alteration.
Keep the trimmed allowance wide — 15 mm — in case it needs letting out again.
Questions people actually ask
Can I take in a lot this way?
A few centimetres per seam, comfortably. Beyond that the armhole and the hem distort and the garment needs recutting.
Do I have to unpick the old seam?
Yes, through the altered section. Leaving two lines of stitching there makes a stiff ridge and the old seam shows.
Last reviewed 2026-08-11