What you need to sew trousers

Sewing trousers requires a sewing machine, thread, needles, scissors, a measuring tape, and pattern paper or a commercial pattern. You will also need pins, a seam ripper for mistakes, and an iron to press seams as you work. If you are altering an existing pair rather than sewing from scratch, you need only the machine, thread, needles, scissors, and measuring tape.

A sewing machine that handles medium-weight fabric is sufficient — you do not need an industrial machine. Thread should match your fabric colour or be a neutral shade like grey or navy. Needles come in sizes; use size 80/12 or 90/14 for cotton and linen, which are the most common trouser fabrics.

Pattern paper or a commercial pattern from a brand like Simplicity, McCall's, or Vogue gives you the pieces to cut. If you are new to sewing, a commercial pattern with detailed instructions is faster than drafting your own. Patterns cost between five and fifteen dollars and come with step-by-step photos.

Key Takeaways

  • Measure your waist, hip, inseam, and rise before cutting, because trousers fit poorly if these measurements are wrong.
  • Sew the inseam and outseam first, then attach the waistband and hem, because this order lets you try them on and adjust length before finishing.
  • Press seams flat with an iron after sewing each section, because this makes the next seam sit properly and the final trousers look professional.
  • Alterations to an existing pair — hemming, taking in the waist, or tapering the leg — take two to four hours and cost less than buying new trousers.

Taking measurements and choosing a pattern size

Measure your waist at the narrowest point, your hip at the fullest point, and your inseam from the inside of your ankle to your crotch. Write these down. Compare them to the size chart on the pattern envelope — most patterns list finished measurements, not your body measurements, so read carefully.

If your measurements fall between two sizes, choose the larger one for the waist and hip, then adjust the inseam length when you cut. Trousers that are too tight in the waist cannot be let out; trousers that are too long can always be hemmed. If you are altering an existing pair, measure the inseam of the trousers as they lie flat, from the crotch seam to the hem.

Cutting fabric and pattern pieces

Lay your pattern pieces on the fabric following the layout diagram in the pattern instructions. Most patterns show a layout for different fabric widths — usually 45 inches or 60 inches — so use the one that matches what you bought. Pin the pattern to the fabric and cut slowly with sharp scissors or a rotary cutter.

You will cut two leg pieces, a waistband, and often a fly facing and pocket pieces. Mark notches and dots on the fabric with tailor's chalk or a fabric pen; these show you where seams meet and help you sew straight. If you are hemming an existing pair, skip this step and move to the hemming section.

Sewing the inseam and outseam

Place the two leg pieces with right sides together — the pretty sides facing each other. Pin the inseam (the seam that runs up the inside of your leg) and sew it with a straight stitch at a quarter-inch seam allowance. Use a seam allowance guide on your machine or mark the line with tape so your stitches stay straight.

Repeat for the outseam (the seam on the outside of your leg). Press both seams flat with an iron, then try the trousers on inside-out to check the fit. If the leg is too tight or too loose, you can adjust the seam allowance on the next pair, but do not unpick these seams unless they are visibly wrong.

Once both legs are sewn, turn one leg right-side-out and tuck it inside the other leg so the right sides face each other. Pin and sew the crotch seam, which connects the two legs. This is the most complex seam because the fabric curves; sew slowly and backstitch at the start and end.

Attaching the waistband and fly

The waistband is a strip of fabric sewn to the top of the trousers. Pin it to the waist opening with right sides together, matching the notches on the pattern. Sew it on, then fold it to the inside and stitch it down by hand or machine. This creates a finished edge that does not fray.

The fly is the opening at the front. Most patterns include a fly facing — a small piece of fabric that reinforces the opening. Sew the facing to the fly opening, then fold and press it. This step takes time but makes the trousers look finished and prevents the opening from tearing.

Add a button and buttonhole at the waist, or use a hook and eye if you prefer. A buttonhole foot on your machine makes this easier; follow your machine's manual for the exact steps.

Hemming the trousers

Try the trousers on right-side-out and mark where the hem should fall — usually at the top of your shoe or just touching the ground. Have someone pin the hem while you stand, or use a hem gauge to mark an even distance all the way around. Cut off excess fabric, leaving half an inch for the hem allowance.

Fold the raw edge up a quarter-inch and press it, then fold it up again to the marked line and press. Pin the hem and sew it with a blind stitch by hand or a blind hem stitch on your machine. A blind stitch is nearly invisible from the outside and looks professional.

If you are altering an existing pair, try them on, mark the new hem length, and cut off the old hem. Fold and press the new hem as described above, then sew it. This takes thirty minutes to an hour per pair.

Fixing common mistakes

If a seam is crooked or puckered, use a seam ripper to remove the stitches and sew again. Seam rippers have a small hook that slides under stitches without cutting the fabric. Work slowly — rushing tears the cloth.

If the waist is too tight after sewing, you can let out the side seams a quarter-inch on each side, which adds half an inch total. If the waist is too loose, take in the side seams or the back seam. Do not alter the inseam or outseam after the legs are sewn, because this changes the fit at the ankle.

If the hem is uneven, unpick it, re-measure, and sew again. Hems are the easiest part to fix, so do not accept an uneven one.

Frequently Asked Questions

Can I sew trousers without a pattern?

You can, but it is much harder. You would need to draft your own pattern by measuring an existing pair of trousers that fit well, then scaling it up or down. For a first pair, a commercial pattern saves time and frustration. Once you have made two or three pairs, you can modify a pattern or draft your own.

What fabric is best for trousers?

Cotton twill, cotton canvas, and linen are the easiest to sew and wear well. Avoid stretchy fabrics like jersey or spandex blends until you have made several pairs, because they require special techniques. Denim works but is thick and hard on sewing machine needles.

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

A first pair takes eight to twelve hours spread over several days, because you will work slowly and check your work often. Once you have made two or three pairs, you can sew a pair in four to six hours. Alterations to an existing pair take two to four hours.

Do I need to use a pattern, or can I copy an existing pair?

You can copy an existing pair by laying it flat, tracing around it on paper, and adding seam allowance. This works well for straightforward styles like straight-leg trousers. For fitted styles or if you want to change the fit, a commercial pattern is more reliable because it accounts for ease — the extra room needed for movement.

What is the hardest part of sewing trousers?

The crotch seam is the hardest because the fabric curves and multiple layers meet at one point. Sew it slowly, backstitch at the start and end, and do not be afraid to unpick and re-sew if it looks wrong. The second hardest part is getting the hem even, which is why trying them on before hemming matters.