Hemming trousers on a sewing machine takes about 30 minutes once you measure and pin

A basic hem on a sewing machine is a straight stitch sewn parallel to the folded edge of the fabric. You measure how much fabric to remove, fold it up, pin it in place, and sew a line about half an inch from the fold. The machine does the work—you guide the fabric. Most trousers need a hem between one-quarter inch and one and a half inches deep, depending on the fabric weight and the look you want.

The whole process works the same whether you are hemming new trousers that are too long or fixing an old hem that has come loose. The main difference is that loose hems sometimes have fraying or damage you will need to trim away first.

Key Takeaways

  • Measure the desired trouser length while wearing the shoes you plan to wear with them, standing on a flat surface, and mark both legs at the same height from the ground.
  • Fold the fabric up to your marked line, pin it every two inches, and try the trousers on to confirm the length before you sew.
  • Thread your machine with thread that matches the trouser color, set it to a straight stitch, and sew parallel to the fold at a consistent distance—usually half an inch.
  • Backstitch at the start and end of each seam to lock the thread, and remove pins as you sew rather than sewing over them.
  • Press the hem flat with an iron after sewing to set the crease and make the hem lie smoothly against the leg.

Measure the length while wearing the shoes you will wear

Put on the trousers with the shoes you plan to wear them with, and stand on a flat, hard floor in front of a mirror. The hem should just touch the top of your shoe or sit about half an inch above it—this is personal preference, but consistency matters more than the exact measurement.

Have someone mark the desired length on both legs with tailor's chalk or a fabric pencil. Mark at the same height on each leg by measuring up from the floor with a ruler or measuring tape. If you are working alone, use a full-length mirror and mark where the hem should fall, then measure that distance from the floor and mark both legs at that measurement.

Write down the measurement from the current hem to your mark on each leg. Trouser legs are sometimes uneven, so measure both sides separately. If one leg is longer than the other by more than a quarter inch, note which one and plan to hem them to different lengths.

Prepare the fabric by trimming and pressing

Fold the trouser leg up along your marked line, with the wrong side of the fabric facing outward. Pin the fold in place every two inches around the leg. Try the trousers on and look in the mirror to confirm the length looks right before you sew—this is your final note to adjust without picking out stitches.

If the original hem is still attached and lies flat under your new fold, you can leave it in place. If it is loose, frayed, or bunched, trim it away with scissors, leaving about a quarter inch of fabric above where you will sew. Press the folded edge with an iron on medium heat to create a sharp crease. This makes the hem easier to sew straight and helps it lie flat when you are done.

Thread the machine and set up for a straight stitch

Wind a bobbin with thread that matches your trousers as closely as possible. Thread the machine following your machine's manual—the path varies by model, but the thread always goes through the tension discs and the needle from front to back. Use a needle size appropriate to your fabric: size 80/12 for lightweight cotton or linen, size 90/14 for medium-weight fabric like twill, and size 100/16 for heavy denim or canvas.

Set the machine to a straight stitch with a stitch length of 2.5 millimeters—this is a standard length that holds well without creating a line of holes. Test the tension on a scrap of folded trouser fabric first. The stitches should look the same on both sides; if the top thread is loose and loopy, increase tension slightly, and if the bobbin thread shows on top, decrease tension.

Sew the hem with the fold as your guide

Position the trouser leg under the presser foot so the fold runs parallel to the needle, about half an inch to the left of it. Lower the presser foot and backstitch three or four stitches to lock the thread. Sew forward slowly, keeping the fold at a consistent distance from the needle—most machines have a line on the throat plate that marks half an inch, which you can use as a guide.

Remove pins as you approach them rather than sewing over them; sewing over a pin can break the needle or damage the machine. Keep your hands relaxed and let the machine feed the fabric—do not pull or push. When you reach the end of the leg, backstitch three or four stitches to lock the thread, then cut the thread and remove the trouser leg from the machine.

Repeat for the other leg, measuring and pinning it the same way. If the legs are different lengths, adjust your starting point so the fold sits at the correct distance from the needle for each leg.

Press and finish the hem

Lay the trouser leg flat on an ironing board with the seam facing up. Press along the seam with an iron on medium heat to set the stitches and flatten the fabric. Flip the leg over and press the hem from the outside to make sure it lies smoothly. This step is important—it sets the crease and makes the hem look finished.

Try the trousers on to check the length and make sure the hem hangs evenly. If the length is wrong, you can pick out the stitches with a seam ripper and re-sew. If the hem puckers or pulls, the tension was too tight; loosen it slightly and re-sew on a new line about a quarter inch away from the first seam.

Common mistakes and how to avoid them

Sewing too close to the fold causes the hem to pucker because the fabric bunches as it folds. Sew at least half an inch from the fold, or even three-quarters of an inch on heavy fabric. Measuring the legs at different heights creates uneven hems; always measure from the floor up, and mark both legs before you fold anything.

Sewing over pins breaks needles and can damage the machine. Remove each pin just before the needle reaches it. Skipping the press step leaves the hem looking wrinkled and unfinished; take two minutes to press after sewing and the hem will look professional. If your stitches are loose or loopy, check the tension and test on a scrap before re-sewing the trouser leg.

Frequently Asked Questions

Can I hem stretch fabrics like knit trousers on a regular sewing machine?

Yes, but use a ballpoint needle (size 80/12 or 90/14) instead of a regular needle, and set the machine to a narrow zigzag stitch instead of a straight stitch. The zigzag allows the fabric to stretch without the seam breaking. Test on a scrap first to make sure the stitch looks right.

What if one trouser leg is longer than the other?

Measure and mark both legs separately from the floor, then hem each one to its own marked line. This is normal—most people's legs are slightly different lengths. Hemming to the same measurement from the floor corrects for this.

How do I fix a hem that came loose after I sewed it?

Pick out the old stitches with a seam ripper, re-press the fold, and sew a new line parallel to the old one, about a quarter inch away. You do not need to remove the old thread completely—just cut it in a few places and pull it out as you sew over it.

Can I use a different color thread if I cannot find an exact match?

Use thread that is one shade darker than the fabric rather than lighter—darker thread is less visible on the finished hem. Test on a scrap of the trouser fabric first. If the contrast is too obvious, consider a neutral color like gray or tan, which blends better than bright colors.

What stitch length should I use for different fabric weights?

Use 2 to 2.5 millimeters for lightweight fabrics, 2.5 to 3 millimeters for medium-weight fabrics, and 3 to 3.5 millimeters for heavy fabrics like denim. Longer stitches are less likely to pucker on heavy fabric. Always test on a scrap first.