The right tension keeps your top thread and bobbin thread balanced in the fabric

Tension is how tightly your sewing machine pulls thread through the fabric. If tension is too tight, fabric puckers and thread breaks. If it is too loose, stitches look loopy and fall apart. The goal is a balanced stitch where the top thread and bobbin thread lock together invisibly inside the fabric layers, with neither one showing on the opposite side.

Most machines have a tension dial numbered 0 to 9, with 4 or 5 as the factory default. Start there. If your stitches look wrong after sewing a test seam, adjust the dial in small steps—usually one number at a time—and test again. The dial controls only the top thread tension; the bobbin tension is rarely touched and requires a screwdriver.

Key Takeaways

  • Balanced tension means the top thread and bobbin thread meet invisibly inside the fabric, with no loops or puckers visible on either side.
  • Start with the dial at the factory default (usually 4 or 5) and test-sew on scrap fabric before starting your project.
  • Increase the number on the dial to tighten the top thread; decrease it to loosen it.
  • Fabric weight, thread type, and needle size all affect how tension looks, so re-test when you change any of these.
  • Bobbin tension rarely needs adjustment and should only be changed by someone comfortable with a screwdriver if stitches still look wrong after adjusting the top dial.

How to test tension before you sew your project

Cut a piece of scrap fabric the same weight as your project fabric—cotton for cotton, knit for knit, and so on. Thread your machine with the same thread you plan to use. Sew a straight line for 3 to 4 inches on the scrap, then remove it and look at both sides.

A balanced stitch looks identical on the top and bottom: a thin, even line with no loops, puckers, or visible thread. If you see the bobbin thread looping on the top side, tension is too loose—turn the dial up by one number. If you see the top thread looping on the bottom side, tension is too tight—turn the dial down by one number. Sew another test line and check again. Most adjustments take two or three tries.

What to do when stitches look loopy on top

Loopy stitches on the top surface mean the bobbin thread is pulling too much, which happens when top tension is too loose. Turn the tension dial up by one number—from 4 to 5, for example—and sew a new test line on scrap fabric.

If the loops are still there after you increase tension, check two other things before adjusting further. First, make sure your needle is inserted all the way into the needle clamp and facing the correct direction for your machine—a backward or loose needle will cause looping even with correct tension. Second, rethread the top thread with the presser foot up, because the presser foot opens the tension discs and lets thread seat properly. If looping continues after these checks, increase tension by another number and test again.

What to do when stitches look loopy on the bottom

Loopy stitches on the bottom surface mean the top thread is pulling too much, which happens when top tension is too tight. Turn the tension dial down by one number—from 5 to 4, for example—and sew a new test line.

Before you adjust further, also check that your bobbin is wound evenly and inserted correctly, because an unevenly wound bobbin or a bobbin sitting crooked in the case will cause bottom loops even with correct top tension. If loops remain after you lower tension and check the bobbin, lower tension by another number and test again. Most machines reach balanced tension within two or three adjustments from the default.

How fabric weight and thread type change what tension you need

Lightweight fabrics like silk or thin cotton often need lower tension (a lower number) because the thread can pull the delicate weave out of shape. Heavy fabrics like denim or canvas usually need higher tension (a higher number) because the thread has to pull harder to lock through thick layers. Always test on a scrap of the actual fabric you are sewing.

Thread type matters just as much. Thick thread like topstitching thread or embroidery thread usually needs lower tension because it takes up more space in the needle and bobbin. Thin thread like machine embroidery thread may need higher tension. Specialty threads like metallic or variegated thread can be unpredictable—test every time you switch. If you change needle size, thread type, or fabric weight, sew a new test line before starting your project.

When to adjust bobbin tension and when to leave it alone

The bobbin tension is set at the factory and rarely needs changing. It lives in a small screw on the bobbin case—the metal or plastic holder that sits inside your machine. Only adjust it if you have already tested the top tension dial thoroughly and stitches still look wrong.

If you do need to adjust bobbin tension, turn the screw only a quarter turn at a time, clockwise to tighten or counterclockwise to loosen. Mark where you started with a pen so you can return to it if something goes wrong. After each quarter turn, wind a fresh bobbin, thread it, and test on scrap fabric. Bobbin tension changes are tiny and straightforward to overshoot. If you are not comfortable with a screwdriver or if adjusting the screw does not fix the problem, take your machine to a repair shop—they can reset it to factory settings if needed.

Common mistakes that look like tension problems but are not

A bent or dull needle causes stitches that look loopy or uneven, and many people adjust tension when they should change the needle instead. Replace your needle before you adjust tension, especially if you have been sewing for more than a few hours or if you hit a pin. A fresh needle costs less than a repair visit.

Lint buildup in the bobbin area also causes tension problems. Brush out lint with a small brush after every project—your machine manual shows where the bobbin sits. Threading mistakes are another common culprit: make sure the presser foot is up when you thread (so the tension discs open), and make sure the thread sits in every guide on its path from the spool to the needle. If you have adjusted tension three or four times and stitches still look wrong, rethread the entire machine from scratch with the presser foot up.

Frequently Asked Questions

What number should my tension dial be on?

Most machines come set to 4 or 5 as the default, and that works for standard cotton thread and medium-weight fabric. Start there and test-sew on scrap fabric. If stitches look unbalanced, adjust by one number at a time until they look even on both sides. Every machine and thread combination is slightly different.

Can I sew without testing tension first?

You can, but you risk wasting fabric and thread if tension is wrong. A test line takes two minutes and saves you from ripping out seams later. Always test when you use a new thread type, change fabric weight, or switch needle size.

Why does my tension look different on knit fabric than on cotton?

Knit fabric stretches and moves differently than woven cotton, so the same tension setting may look unbalanced. Test on a scrap of the actual fabric you are using. You may need to lower tension slightly for knit to prevent puckering, but this varies by machine and thread.

Is it normal to adjust tension every time I sew?

Not every time, but yes when you change thread type, fabric weight, or needle size. If you sew the same weight fabric with the same thread repeatedly, you can usually leave tension where it is. Write down the number that works for your most common setup so you have a starting point.

What happens if I turn the tension dial all the way to 9?

Very tight tension can break thread, pucker fabric, and strain your machine. If you accidentally turn it too high, turn it back down to 4 or 5 and test again. There is no number that works for all fabrics and threads, so extreme settings are usually a sign something else needs checking—like the needle or threading.