Basic underwear construction uses just four seams and elastic

Sewing underwear is simpler than most garments because the pieces are small, the seams are few, and the fit tolerates small mistakes. A basic brief or boxer brief needs only a front panel, a back panel, two side seams, a waistband seam, and leg openings finished with elastic. You do not need a serger, a coverstitch machine, or advanced skills—a regular sewing machine and ballpoint needles are enough.

The main difference between sewing underwear and sewing a shirt is that underwear uses ballpoint or stretch needles instead of universal needles, because the fabric moves and you need the needle to slide between fibers rather than pierce them. You will also use elastic instead of a zipper or buttons, and you will finish seams with a zigzag stitch or a narrow seam allowance to keep them from bunching under clothes.

Most people start with a pattern from a pattern company like Simplicity, McCall's, or Butterick, or from independent designers on Etsy. A pattern tells you how big to cut each piece, where to sew them, and what size elastic to use. Without a pattern, you are measuring and drafting from scratch, which is harder.

Key Takeaways

  • You need a pattern, ballpoint needles, stretch fabric (usually nylon or spandex blend), and elastic in the width and length your pattern specifies.
  • The basic construction order is: sew the front and back panels to the side panels, attach the waistband elastic, then finish the leg openings with elastic.
  • Ballpoint needles prevent runs and laddering in stretch fabric, and a zigzag stitch keeps seams from rolling or bunching.
  • Most underwear patterns take two to four hours from cutting to finished garment, including time to wind bobbins and press seams.

What fabric and notions you need

Fabric for underwear is almost always a knit with at least 15 percent spandex or elastane. Nylon-spandex blends are the most common and the easiest to sew. Cotton-spandex blends exist but are less stretchy and less forgiving. Avoid woven fabric—it will not stretch and will tear at the seams. Most patterns call for 0.5 to 1 yard of fabric, depending on the size and style.

Elastic comes in different widths: 0.5 inch for leg openings, 1 inch for waistbands on briefs, and 1.5 inches for waistbands on boxer briefs or high-waist styles. Your pattern will tell you the width and the length you need. Do not guess—elastic that is too loose will roll down, and elastic that is too tight will dig in. Buy the length the pattern specifies, then subtract 0.5 to 1 inch and test the fit on your body before you sew it into the garment.

You will also need ballpoint needles (size 75/11 or 80/12 for most knits), polyester or nylon thread in a color that matches your fabric, and scissors or a rotary cutter to cut the pattern pieces. A serger is not necessary—a zigzag stitch on a regular machine works fine.

How to cut and prepare your pattern pieces

Lay your pattern pieces on the fabric according to the layout diagram in the pattern instructions. Most patterns show you how to arrange the pieces to use the least fabric. Pin the pattern to the fabric and cut slowly with sharp scissors or a rotary cutter. Knit fabric can shift, so use enough pins or weights to hold it flat.

Mark the notches and any construction marks (like where to attach elastic) with a fabric pen or tailor's chalk. These marks tell you where seams meet and where to start and stop stitching. If your pattern includes a grainline arrow, align it with the direction of the stretch in the fabric—usually the most stretch runs across the width of the fabric, not up and down.

Once you have cut all the pieces, lay them out in the order you will sew them. Most patterns have you sew the side seams first, then attach the waistband, then finish the leg openings. Organizing your pieces in that order keeps you from sewing the wrong seams together.

Sewing the side seams and crotch

Place the front and back panels with the right sides together (the pretty sides facing each other). Sew the side seams using a 0.5-inch seam allowance and a straight stitch. Use a ballpoint needle and polyester thread. Sew slowly and let the machine feed the fabric—do not pull or push. Stretch fabric can bunch if you force it through the presser foot.

After you sew the side seams, sew the crotch seam. This is the seam that runs from the front waistband, between the legs, to the back waistband. Use the same stitch and seam allowance. Backstitch at the beginning and end to lock the stitches.

Once the main seams are sewn, trim the seam allowances to 0.25 inch and finish them with a zigzag stitch to prevent the fabric from rolling or laddering. Set your machine to a narrow zigzag (width 2 to 3, length 2 to 3) and stitch along the edge of each seam allowance. This keeps the seams from curling when you wash and wear the underwear.

Attaching the waistband elastic

Cut your elastic to the length your pattern specifies, minus 0.5 to 1 inch. Join the ends of the elastic by overlapping them 0.5 inch and sewing them together with a zigzag stitch. This creates a loop.

Divide the elastic loop and the waistband opening into four equal sections and mark them with pins. This keeps the elastic from bunching on one side. Pin the elastic to the wrong side of the waistband (the inside of the garment), matching the pins. The elastic should be flat against the fabric, not stretched yet.

Sew the elastic to the waistband using a zigzag stitch, stretching the elastic as you sew so it lies flat. Start at one pin and sew to the next, stretching the elastic to match the waistband length. The zigzag stitch allows the elastic to move and recover without breaking. Sew around the entire waistband, then fold the elastic to the inside and topstitch if you want a finished look.

Finishing the leg openings

Cut two pieces of 0.5-inch elastic, each the length your pattern specifies minus 0.5 inch. Join the ends of each piece with a zigzag stitch to make two loops. Divide each loop and each leg opening into four sections and mark with pins.

Pin the elastic to the wrong side of each leg opening, matching the pins. Sew the elastic using a zigzag stitch, stretching as you go, just as you did with the waistband. The leg openings should curve smoothly and lie flat against your skin when you wear the underwear.

Once the elastic is sewn, try on the underwear inside-out to check the fit. The waistband should sit at your natural waist without digging in, and the leg openings should not roll or gap. If the fit is wrong, you can remove the elastic with a seam ripper and re-sew it tighter or looser.

Pressing and final details

Turn the underwear right-side out and press all the seams flat with a warm iron. Do not use high heat on spandex—it can melt. Press the waistband and leg openings so the elastic lies flat and the seams are crisp.

If you want a more finished look, topstitch 0.125 inch away from the waistband seam and the leg opening seams. This holds the elastic in place and creates a professional appearance. Use a straight stitch and the same thread color as the elastic.

Wash the underwear in warm water with mild detergent before you wear it. This removes any loose threads and helps the fabric and elastic settle into their final shape. Dry on low heat or hang-dry to extend the life of the spandex.

Frequently Asked Questions

What if my seams keep bunching or puckering?

Bunching usually means you are using the wrong needle or pulling the fabric. Switch to a ballpoint needle and let the machine feed the fabric without pushing or pulling. Also check that your thread tension is not too tight—if the top thread is pulling the bottom thread to the surface, loosen the top tension dial slightly.

Can I use a regular needle instead of a ballpoint needle?

You can, but you risk laddering and runs in the fabric. A regular needle pierces the fibers, which can break them in stretch fabric. A ballpoint needle slides between the fibers and is designed for knits. The cost difference is small and the result is much better.

How do I know if my elastic is the right length?

Wrap the elastic around your waist or leg (depending on which opening you are measuring) and pull it snug but not tight. It should feel comfortable and not dig in. Subtract 0.5 to 1 inch from that measurement and sew it into the garment. You can always remove and re-sew it if the fit is not right.

Do I need a serger to sew underwear?

No. A serger creates a neater finish, but a regular sewing machine with a zigzag stitch works fine. Zigzag the seam allowances after you sew the main seams and the underwear will hold up through many washes.

What is the difference between a brief and a boxer brief pattern?

A brief covers from the waist to the top of the thigh and has a straightforward two-piece front and back. A boxer brief extends down the leg and usually has four pieces: front, back, and two leg panels. Boxer briefs take longer to sew because of the extra seams, but the construction is the same.