Sewing underwear is simpler than most garments because the pieces are small and the seams are straightforward

Underwear requires only four basic pieces — front, back, and two side panels — sewn together with elastic at the waist and leg openings. The construction is nearly identical whether you are making briefs, boyshorts, or bikini-cut styles; the only real difference is the shape of those four pieces. You do not need a serger, a coverstitch machine, or special thread. A regular sewing machine, ballpoint needles, and stretch thread or regular polyester thread will work. The seams do not need to be as neat as a dress seam because they sit against skin and will not be seen.

Most sewers start with a commercial pattern because drafting underwear from scratch requires understanding how much ease (extra room) to build in, and that varies by fabric and body shape. Patterns from companies like Simplicity, McCall's, and independent designers on Etsy come with all four pieces already drawn to size, a materials list, and step-by-step photos. A pattern costs between $5 and $15 and can be printed at home or ordered as paper.

Key Takeaways

  • Underwear patterns come in four pieces — front, back, and two sides — and most sewers use a commercial pattern rather than drafting their own.
  • Ballpoint needles prevent runs in stretch fabric, and stretch thread or regular polyester both work; a serger is not required.
  • Seams are sewn with a straight stitch and finished with elastic at the waist and leg openings, which is the most time-consuming step.
  • Fit depends on how much ease you add when cutting and which elastic width you choose; most patterns assume a specific elastic type.

Choosing a pattern and fabric

Underwear patterns are usually labeled by style — brief, boyshort, bikini, thong — and by size range. Most patterns cover sizes XS to XL on a single sheet, with different cutting lines for each size. Before you buy, check whether the pattern is designed for knit fabric (which stretches) or woven fabric (which does not). Nearly all underwear patterns assume knit, usually a nylon-spandex blend or cotton-spandex blend. Woven patterns exist but are less common.

Fabric choice affects how the finished underwear feels and lasts. Nylon-spandex is the standard for commercial underwear because it is smooth, dries quickly, and holds its shape through many washes. Cotton-spandex is softer and more breathable but slightly less durable. Microfiber (a synthetic) is silky and thin but can pill with friction. Most fabric stores sell underwear-weight knits in the stretch or activewear section. You will need between one-quarter and one-half yard depending on the size and style.

Gathering materials and preparing to cut

Beyond fabric and a pattern, you need elastic, thread, and a needle. Elastic comes in widths from 0.5 inches to 1.5 inches; most underwear patterns specify which width to use, and using the wrong width will change the fit. Common widths are 0.75 inches for the waist and 0.5 inches for the leg openings, though this varies. Buy the elastic type the pattern calls for — usually fold-over elastic (which wraps around the edge) or lingerie elastic (which sits on top of the fabric).

Prepare your fabric by washing and drying it the way you will wash the finished underwear, because knit fabric shrinks slightly. Lay it flat and let it relax for a few hours before cutting. Pin your pattern pieces to the fabric following the grain line marked on the pattern — this line should run parallel to the selvage (the finished edge). Cut slowly and carefully; a rotary cutter and self-healing mat make this easier than scissors, but scissors work fine if you are patient.

Sewing the side seams and center seams

Start by sewing the two side seams that connect the front and back panels. Place the front and back pieces right sides together (the pretty sides facing each other) and pin along one side seam. Use a ballpoint needle in your machine — this needle has a rounded tip that slides between fibers in stretch fabric rather than piercing them, which prevents runs. Sew with a straight stitch at a standard length (2.5 mm) and a standard tension setting.

Sew the first side seam, remove the pins, and repeat on the other side. Then sew the center seam that closes the crotch, again with right sides together. These three seams are the skeleton of the underwear. At this point you have a tube with an open waist and open leg holes. Do not trim the seam allowances yet; they will be covered by the elastic.

Attaching elastic at the waist

Elastic attachment is where most of the time goes, and it is where fit is determined. Measure around your waist where you want the underwear to sit. Subtract 1 to 2 inches from that measurement — the elastic should be slightly smaller than the opening so it pulls the fabric in. Cut your elastic to that length and join the two ends by overlapping them 0.5 inches and sewing back and forth across the overlap with a zigzag stitch. You now have an elastic loop.

Divide both the elastic loop and the waist opening into four equal sections and mark them with pins. Pin the elastic to the wrong side of the fabric (the side that will be against your skin) at those four points, then fill in with more pins every inch or so. The elastic should lie flat against the fabric, not stretched. Using a zigzag stitch set to medium width and length, sew the elastic to the fabric, stretching the elastic gently as you sew so the fabric gathers evenly onto it. When you reach the end, the fabric should be gathered and the elastic should lie flat.

Attaching elastic at the leg openings

Repeat the same process for each leg opening. Measure around the leg hole, subtract 0.5 to 1 inch, and cut elastic to that length. Join the ends with a zigzag stitch, divide into four sections, pin, and sew with a zigzag stitch while stretching the elastic gently. The leg openings are smaller, so this step goes faster than the waist.

Once both leg openings are done, try the underwear on inside-out to check the fit. The elastic should sit comfortably without digging in or sliding down. If the waist is too tight, you can carefully cut the elastic seam, remove a small section of elastic, rejoin the ends, and re-sew. If it is too loose, the fix is more difficult — you would need to remove the elastic, cut a shorter piece, and start over. This is why measuring carefully before you sew is worth the time.

Finishing the seams and washing

Underwear seams do not need to be finished with a serger or binding because they are small and will not fray noticeably against skin. If you want a neater look, you can trim the seam allowances to 0.25 inches with pinking shears (which cut a zigzag edge that resists fraying) or a rotary cutter. Many sewers skip this step entirely.

Turn the underwear right-side out and try it on. The fit should be snug but not tight, and the elastic should not roll or dig in. Wash in cool water with mild detergent and lay flat to dry, or tumble dry on low. Underwear made from nylon-spandex or cotton-spandex will last 50 to 100 washes with normal care. Avoid fabric softener and bleach, which break down the elastic and fibers.

Common mistakes and how to avoid them

The most common mistake is using the wrong needle. A regular universal needle will catch and break threads in stretch fabric; a ballpoint needle prevents this. The second mistake is sewing the elastic too tightly. If you stretch the elastic while sewing and do not stretch the fabric to match, the fabric will bunch and the elastic will dig in. Sew with the elastic relaxed and let it do the gathering.

A third mistake is choosing elastic that is too wide or too narrow for the pattern. If the pattern calls for 0.75-inch elastic and you use 1-inch elastic, the waist will sit differently and may roll. If you cannot find the exact width, a slightly narrower elastic is safer than a wider one. Finally, do not skip the wash-and-dry step before cutting. Fabric shrinks, and cutting before that happens means the finished underwear will be smaller than intended.

Frequently Asked Questions

Do I need a serger to sew underwear?

No. A regular sewing machine with a straight stitch and a zigzag stitch is all you need. A serger makes seams look more finished, but underwear seams are hidden and do not need to be perfect.

What thread should I use?

Polyester thread works fine. Stretch thread is slightly better for seams that will move a lot, but most sewers use regular polyester without problems. Use a color that matches your fabric or elastic.

Can I use regular elastic instead of lingerie elastic?

It depends on the pattern. If the pattern specifies fold-over elastic, regular elastic will not wrap around the edge the same way. If it specifies lingerie elastic, regular elastic may be too stiff. Check the pattern before you buy.

How much fabric do I need?

Most underwear patterns use between one-quarter and one-half yard. Check your specific pattern's materials list; the amount depends on your size and the style.

Why does my underwear feel tight after washing?

Knit fabric shrinks slightly in the wash. Wash and dry your fabric before cutting to prevent this. If the finished underwear is too tight, the elastic may also be too small — check your measurement and elastic length.