How to Sew Underwear for Women | Stretch-Seam Basics

Making your own underwear is worth learning if you’re tired of seams that dig in or waistbands that roll. You cut knit fabric with the stretch going the right way, sew seams that flex, and finish with elastic stretched evenly around the openings. A sewing machine with a zigzag or stretch stitch gets the job done — a serger makes it faster but isn’t required. The project takes a couple of hours per pair once pieces are cut. Work in this order: copy a pair you like, cut fabric, build the crotch, join the sides, then finish with elastic.

What You Need To Cut And Sew Underwear

Gather four things: stretch fabric, elastic, a ballpoint needle, and matching thread. Peekaboo Pattern Shop’s guidance calls for a ballpoint needle in size 70/10 or 80/12, which parts knit fibers instead of piercing them, preventing skipped stitches and snags. For fabric, choose a stretch knit, cotton jersey, or stretch lace, plus a small piece of cotton jersey for the gusset lining.

Your machine needs a stretch stitch, a zigzag, or serger capability. Straight stitches pop under tension — the main reason homemade underwear fails. Test your stitch on a scrap before cutting into your good fabric.

The Build Order: Gusset, Sides, Then Elastic

Start with a pattern you trust. Trace a well-fitting pair of briefs by flattening the garment and drawing around each piece, or use a free pattern like Acacia by Megan Nielsen or the Women’s Underwear Pattern from Peekaboo Pattern Shop. Cut pieces on the fold where indicated, keeping the fabric’s greatest stretch running across the body, not up and down.

Assemble the gusset first. Sandwich the front and back panels between the gusset layers with right sides together, sew with a zigzag or serger, then turn so seam allowances are enclosed. Track which side is front — the crotch is easy to reverse. Join the side seams next, right sides together, using the same stretch stitch. Then move to elastic. Mark elastic and fabric into quarters and pin together — this distributes stretch evenly and stops bunching.

Common Mistakes And The Fit Test

Three errors cause most failed pairs: cutting against the grainline, using a non-stretch stitch, and rushing the elastic.

• Wrong stretch direction. Knit fabric stretches more one way than the other. Cut every piece so the greater stretch runs side to side, or the waistband will ride up and legs will gap.
• Straight stitching. A plain straight stitch has no give, so seams break the first time you bend. Use zigzag, stretch stitch, or serger only.
• Uneven elastic. Skipping quarter-mark pins means elastic ends up tighter on one side. Mark and pin every time.

Try the underwear on before trimming seam allowances or topstitching. Fit adjustments are simple at this stage — taking in a side seam takes minutes, but redoing elastic after trimming is a full redo. Check gusset position and leg openings now.

The fabric you choose matters as much as your stitching. If you’re unsure which knit will hold up best, our breakdown of the best fabric for underwear compares cotton jersey, bamboo, and modal options so you buy the right material the first time.

Finishing Steps For A Professional Look

Once the fit is right, finish the job: trim excess fabric close to the stitching line, then topstitch seam allowances and elastic ends so they lie flat. Fold elastic to the inside and stitch it down with a zigzag for a fully enclosed waistband; some prefer leaving it exposed on the wrong side, which is fine for everyday pairs.

Your first pair will take longer than your fifth. The learning curve is mostly in the elastic — once you’ve got the even-stretch technique down, a pair takes under an hour from cut to finish. Wash like any delicate knit and they’ll hold up through many wears.