What You Need to Sew Underwear

Sewing underwear is simpler than most garments because the pieces are small, the seams are straightforward, and you do not need closures or complicated shaping. You will need a sewing machine (even a basic one works), thread that matches your fabric, elastic for the waistband and leg openings, and fabric—usually cotton knit, jersey, or a blend designed for underwear. A pattern is essential; you can buy one from Simplicity, McCall's, or Butterick, or read one from sites like Etsy or Craftsy. A measuring tape, scissors, pins, and a serger or zigzag stitch (to prevent fraying on knit fabric) round out the basics.

The most important choice is fabric. Underwear needs to stretch and breathe, so avoid rigid wovens. Cotton jersey, cotton-spandex blends, and nylon are standard. Most patterns specify the weight and type, so follow that guidance. Elastic comes in different widths—typically 1 inch for waistbands and narrower widths for leg openings—and you will need to know your waist and hip measurements before you buy.

Key Takeaways

  • Underwear patterns come in standard sizes and require only your waist and hip measurements to choose the right size.
  • Knit fabrics (cotton jersey, cotton-spandex blends) are essential because they stretch; woven fabrics will tear and feel stiff.
  • The main seams are the side seams and the crotch seam, both sewn with a zigzag or serger stitch to prevent fraying.
  • Elastic is attached to the waistband and leg openings using a casing method or direct process, and the width matters for comfort and fit.
  • A finished pair takes two to four hours for a beginner, including cutting, sewing, and finishing the elastic.

Choosing and Preparing Your Pattern

Start by selecting a pattern designed for underwear, not a general garment pattern. Simplicity, McCall's, and Butterick all publish underwear patterns in a range of styles—briefs, boyshorts, thongs, and bikinis. Look at the envelope or listing to find your size. Most patterns use standard sizing (XS to XL or numbered sizes), and you choose based on your waist measurement. If you are between sizes, pick the larger one; you can always take in the side seams.

Once you have the pattern, lay out all the pieces and read the instruction sheet before you cut fabric. Underwear patterns typically include a front panel, back panel, and sometimes separate gusset pieces for the crotch. The sheet will tell you how much fabric to buy (usually 1 to 1.5 yards), how to lay out the pieces to avoid waste, and which direction the stretch should run. Mark the stretch direction on your fabric with a pen or chalk before you cut—this matters because the fabric must stretch across the body, not lengthwise.

Cutting and Marking Your Fabric

Lay your fabric on a flat surface with the pattern pieces pinned down. Use sharp scissors or a rotary cutter to cut slowly and cleanly; ragged edges on knit fabric will fray more easily. Cut all the pieces at once—front, back, gusset if included, and any waistband pieces. Most patterns include a seam allowance (usually half an inch), so cut along the pattern line exactly.

After cutting, use a fabric pen or tailor's chalk to mark the notches and dots on the pattern. These marks show you where seams meet and where elastic will be attached. Transfer them to your fabric by making small marks on the wrong side (the side that will be hidden). Do not skip this step; the marks keep your seams aligned and your elastic evenly distributed.

Sewing the Main Seams

Start by sewing the side seams. Place the front and back panels with right sides together (the pretty sides facing each other), pin along the side edge, and sew with a zigzag stitch set to a medium width and length. A zigzag stitch stretches with the fabric and prevents the seam from breaking when you wear the underwear. If you have a serger, use a 4-thread or 3-thread overlock stitch instead—it is faster and more professional-looking. Sew both side seams, then try the underwear on inside-out to check the fit. The leg openings should sit snugly on your thigh without cutting off circulation.

Next, sew the crotch seam. If your pattern includes a separate gusset piece, sew it to the front panel first, then attach the back panel. If not, sew the front and back panels together at the crotch. Again, use a zigzag or serger stitch. This seam takes the most stress, so make sure it is find. Backstitch at the beginning and end of every seam to lock the stitches.

Trim any loose threads and try the underwear on again inside-out. The fit should be snug but not tight, and the crotch seam should sit in the right place. If the leg openings are too loose or too tight, you can adjust them when you attach the elastic.

Attaching Elastic to the Waistband

There are two ways to attach elastic: the casing method (where you fold the fabric over the elastic) and the direct method (where you sew the elastic directly to the edge). The casing method is more comfortable and is standard for most patterns. Fold the top edge of the underwear down by half an inch, wrong sides together, and sew a straight stitch close to the fold. This creates a tunnel. Cut a piece of elastic to fit your waist snugly (usually 1 to 2 inches smaller than your actual waist measurement), pin it inside the tunnel, and sew it down with a zigzag stitch, stretching the elastic as you sew so it lies flat.

If your pattern calls for the direct method, pin the elastic to the right side of the fabric at the waistband edge, then sew it down with a zigzag stitch, stretching the elastic as you go. Fold the elastic to the wrong side and sew again to find it. This method is faster but less forgiving if your tension is off.

Finishing the Leg Openings

Attach elastic to the leg openings the same way you did the waistband. Cut two pieces of elastic, each about 1 to 2 inches smaller than the leg opening measurement. Pin one piece to each leg opening, right sides together, and sew with a zigzag stitch while stretching the elastic. The elastic should gather the fabric slightly so the leg opening hugs your thigh without rolling or riding up.

If you used the casing method for the waistband, you can use it here too: fold the leg opening edge inward, create a tunnel, and thread the elastic through. This takes longer but gives a very neat finish. For speed, the direct method works fine—just make sure your zigzag stitch is wide enough to stretch with the fabric.

After attaching all the elastic, try the underwear on right-side-out. It should feel snug and comfortable, with no pinching or gaps. If the waistband or leg openings are too tight, you can carefully cut a small slit in the casing and remove some elastic. If they are too loose, you can add a second row of stitching to tighten the elastic.

Final Touches and Troubleshooting

Trim all loose threads and turn the underwear right-side-out. Wash it in warm water with mild detergent before wearing to remove any marking pen and to preshrink the fabric. Dry on low heat or lay flat to dry. If the seams pucker or the fabric bunches, it usually means your tension was too tight or you used the wrong stitch. Knit fabrics need a stretch stitch; a regular straight stitch will snap when you move.

If the crotch seam feels uncomfortable or the gusset is too small, you can add a second gusset layer for more coverage. If the waistband rolls or digs in, the elastic is probably too tight; remove it and replace it with a slightly wider piece or a lower-tension elastic designed for underwear. These adjustments are normal on your first pair—keep notes so your second pair fits better.

Frequently Asked Questions

What is the difference between a serger and a regular sewing machine for underwear?

A serger trims and finishes the seam edge in one pass, which is faster and looks more professional. A regular machine with a zigzag stitch does the same job but in two steps—sew the seam, then trim. Both work; a serger is a luxury, not a requirement.

Can I use regular cotton fabric instead of knit?

Regular woven cotton will tear at the seams when you move because it does not stretch. Knit fabric is essential for underwear. If you cannot find knit at your local fabric store, order it online from Mood Fabrics, Joann, or a specialty knit supplier.

How much elastic do I need?

Measure your waist and each leg opening, then subtract 1 to 2 inches from each measurement. This creates the snug fit that keeps underwear in place. Write down these numbers before you shop so you buy the right length.

What if my seams keep breaking when I wear the underwear?

You are probably using a straight stitch on knit fabric. Switch to a zigzag stitch with a medium width (about 2 to 3 mm) and length (about 2 to 3 mm). This stitch stretches with the fabric instead of snapping. If you have a serger, use that instead.

How long does it take to sew a pair of underwear?

A beginner usually takes two to four hours for the first pair, including cutting, sewing, and attaching elastic. Once you have made a few pairs, you can finish one in an hour or less. The time depends on how carefully you mark and pin, and whether you use a serger.