Hemming knit pants is different from hemming woven fabric because knits need to move with your leg

Knit pants stretch, so a rigid hem will pull and pucker. The best approach is a flexible stitch that moves with the fabric—either a ballpoint needle on a sewing machine with a stretch stitch, or a hand-sewn method that lets the hem give a little. You do not need special equipment, but you do need to choose the right technique for how much the pants move.

The two main routes are machine-hemming with a stretch stitch (faster, holds up through many washes) and hand-hemming with a flexible stitch like a catch stitch (slower, invisible, best for fine knits). Both work. Machine hemming is practical for everyday pants; hand hemming is worth the time if the pants are expensive or the fabric is delicate.

Key Takeaways

  • Knit hems need to stretch, so a regular straight stitch will snap and pucker—use a ballpoint needle and a stretch stitch on the machine, or hand-sew with a catch stitch.
  • Try on the pants and mark the hem length while wearing the shoes you will wear with them, then fold and pin the hem before measuring.
  • A 1-inch hem is standard for knits; fold the raw edge under once and stitch it down rather than folding twice like you would with woven fabric.
  • Test your stitch on a scrap of the same knit fabric first to make sure it stretches without breaking.
  • Wash and dry the pants before hemming if they have never been washed, because knits can shrink unpredictably.

Prepare the pants and mark the hem length

Put on the pants with the shoes you plan to wear them with. Stand in front of a mirror and have someone pin the hem at the length you want, or use a measuring tape to mark where the hem should fall—usually at the top of your shoe or just touching it. The hem should be even all the way around the leg.

Take the pants off and measure from the pin or mark down to the raw edge of the pant leg. Write this number down. If the measurement is uneven around the leg (common with knits that have shifted), trim the leg to make it even before you hem. A rotary cutter and a ruler work well for this; a pair of sharp scissors works too, but takes longer.

Choose between machine hemming and hand hemming

Machine hemming with a stretch stitch is the faster choice and holds up well through repeated washing. You will need a sewing machine with a stretch stitch setting (most machines made in the last 20 years have one), a ballpoint needle, and thread that matches the pants. The stretch stitch looks like a zigzag and gives the hem room to move. This method takes 15 to 20 minutes per pant leg.

Hand hemming with a catch stitch is slower but invisible from the outside and works on any fabric weight. It takes 30 to 45 minutes per leg but is the best choice if the pants are delicate or if you want the hem to be completely invisible. A catch stitch is a loose zigzag you make by hand, moving the needle through the fold of the hem and then catching just one or two threads of the pant leg itself.

Fold and pin the hem

Fold the raw edge of the pant leg up by half an inch and press it with an iron on a low setting (knits can melt on high heat). This creates a clean edge and keeps the fold in place while you work. Do not fold the hem twice like you would with woven fabric—one fold is enough for knits and keeps the hem from being too bulky.

Now fold the hem up to the length you marked earlier. Pin it in place every 2 to 3 inches around the leg, keeping the fold even. Try the pants on to double-check the length before you stitch. If the length is off, unpin and adjust.

Machine hem with a stretch stitch

Insert a ballpoint needle into your machine—this is crucial. A ballpoint needle slides between the fibers of the knit instead of piercing them, which prevents runs and snags. Set your machine to a stretch stitch (often called a "lightning bolt" stitch or labeled as "stretch"). Set the stitch length to 2.5 to 3.0 mm and the width to 2.0 to 2.5 mm. Test the stitch on a scrap of the same knit fabric first.

Sew along the fold of the hem, keeping the needle about a quarter inch from the fold. Sew slowly and let the machine do the work—do not pull the fabric. When you reach a corner, stop with the needle down, lift the presser foot, turn the fabric, lower the presser foot, and continue. Backstitch at the start and end to lock the thread.

After you finish, try the pants on and check that the hem lies flat and does not pucker. If it does pucker, the stitch was too tight or you used the wrong needle. Rip it out and try again with a slightly wider stitch or a true ballpoint needle.

Hand hem with a catch stitch

Thread a needle with thread that matches the pants and tie a knot at the end. Start inside the fold of the hem so the knot is hidden. Bring the needle out through the fold, then catch just one or two threads of the pant leg itself—not all the way through to the outside. Move the needle back into the fold about a quarter inch away and slide it along inside the fold for a quarter inch, then come back out and catch the pant leg again. This creates a loose zigzag that stretches with the fabric.

Keep the stitches loose and even, about a quarter inch apart. The looser the stitch, the more the hem will stretch. Work your way around the entire leg, then tie off the thread inside the fold. A catch stitch is invisible from the outside because you are only catching a thread or two of the pant leg, not going all the way through.

Finish and wash the pants

Trim any loose threads and try the pants on one more time. Walk around and bend your knees to make sure the hem does not pull or pucker. If the hem looks good, you are done.

Wash and dry the pants normally. Knit hems hold up well through many washes if you used the right stitch. If the hem starts to come loose after several washes, it usually means the stitch was too tight or you used a regular needle instead of a ballpoint. You can re-stitch it using the same method.

Frequently Asked Questions

Can I use a regular straight stitch to hem knit pants?

A regular straight stitch will eventually snap because knits stretch and a rigid stitch cannot move with them. You will see puckering and broken threads after a few wears or washes. A stretch stitch or catch stitch is worth the extra time.

What if I do not have a ballpoint needle?

A ballpoint needle is the best choice, but if you do not have one, a universal needle is the next option. Avoid sharp needles, which can split the fibers and cause runs. Ballpoint needles cost a few dollars and come in packs of five or ten.

How much hem allowance do I need?

One inch is standard for knit pants. Fold the raw edge up by half an inch, then fold the hem up to your marked length. This gives you a half-inch hem allowance, which is enough to hold the stitch without being bulky.

Can I hem stretchy knits like spandex blends?

Yes, but use an even looser stitch than you would for regular knits. Spandex blends need more give, so a hand-sewn catch stitch or a very wide machine stretch stitch works best. Test on a scrap first to make sure the stitch does not break when you pull the fabric.

What if the hem puckers after I wash the pants?

Puckering usually means the stitch was too tight or the needle was wrong. Rip out the hem and try again with a looser stitch width, a slower machine speed, or a hand-sewn catch stitch. If the puckering is minor, you can often smooth it out by gently stretching the hem while it dries.