If your sewing machine suddenly starts producing horrible-looking stitches, it is very tempting to reach straight for the tension dial.
Loops underneath? Tension.
Skipped stitches? Tension.
Thread breaking? Tension.
Except quite often, the tension is not actually the first thing that needs changing.
A sewing machine can produce untidy stitches for all sorts of very ordinary reasons: incorrect threading, a damaged needle, the wrong bobbin, poor-quality thread or a surprising amount of fluff hiding around the bobbin area.
So before you start turning tension dials and creating an entirely new problem, it is worth doing a few simple checks first.
If you’re still getting to grips with your machine, our sewing for beginners guide covers some of the common mistakes worth knowing about.
What Does Sewing Machine Tension Actually Do?
Sewing machine tension controls how the upper thread and bobbin thread work against each other as each stitch is formed.
On a correctly formed lockstitch, the upper thread passes through the fabric, catches the bobbin thread and the two threads lock together. Ideally, that meeting point sits within the layers of fabric rather than being pulled noticeably towards the top or bottom.
When the tension is balanced, the stitches should look neat and even. You should not have obvious loops on either side, and one thread should not be dragging the other completely through the fabric.
If the upper tension is too tight, the bobbin thread may become visible on the top of the fabric. If the upper tension is too loose, the upper thread may form loose stitches or loops on the underside.
That sounds straightforward enough, but there is an important catch.
Loose stitches underneath do not automatically mean the tension setting itself is wrong. If the upper thread has missed the tension discs or take-up lever, for example, the machine may behave as though there is virtually no upper tension at all.
That is why I would always check the basics before changing a setting that may have been perfectly correct in the first place.
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How Do I Know If My Sewing Machine Tension Is Wrong?
A genuine tension problem tends to produce a consistent imbalance between the upper and bobbin threads.
You may notice that:
- the bobbin thread is being pulled onto the top of the fabric;
- the upper thread is being pulled towards the underside;
- stitches look noticeably different on the two sides of the fabric;
- the problem continues after the machine has been correctly rethreaded;
- a fresh, suitable needle does not solve it; or
- changing fabric or thread has altered how the stitch forms.
What I would not do is diagnose every sewing problem as tension.
Skipped stitches, snapped thread, bunching underneath and uneven stitching can all have other causes. Treat the tension dial as part of the troubleshooting process rather than the emergency button for anything unpleasant happening near the needle.
5 Things to Check Before Changing the Sewing Machine Tension
1. Rethread the Machine Properly
This is usually my first step.
And I mean properly rethread it from the beginning, rather than pulling the thread out of the needle and putting it back in again.
Raise the presser foot before threading the upper thread. On many sewing machines, lifting the presser foot releases or opens the upper tension system so the thread can sit correctly between the tension discs.
Then follow the machine's complete threading path from the spool to the needle.
Pay particular attention to the thread guides and take-up lever. Missing one small part of the threading route can produce a remarkably dramatic mess underneath an otherwise innocent-looking piece of fabric.
Also make sure the presser foot is lowered again before you start sewing.
If your machine was sewing perfectly well five minutes ago and suddenly isn't, a complete rethread is a much more sensible first move than immediately changing the tension.
2. Check the Sewing Machine Needle
Next, have a look at the needle.
A blunt, bent or damaged needle can cause skipped stitches, damaged fabric, thread breakage and generally miserable-looking sewing.
Check that the needle:
- is the correct type for the fabric you are sewing;
- is an appropriate size for the fabric and thread;
- has not become bent or blunt; and
- is inserted fully and in the correct direction for your machine.
Different fabrics can need different needles. A standard woven cotton, a stretchy jersey and a heavy denim are not necessarily going to behave happily with exactly the same needle.
If I am troubleshooting and cannot remember how long a needle has been in the machine, I will often simply replace it.
Needles are considerably cheaper than an afternoon spent arguing with a sewing machine.
If needle choice is where you’re getting stuck, Choosing the Correct Sewing-Machine Needle should help.
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3. Check the Thread
Thread can cause more problems than you might expect.
Old, brittle, damaged or poor-quality thread may snap, shred or feed unevenly through the machine. Even perfectly decent thread can cause trouble if it is catching somewhere between the spool and the needle.
Check that the thread can unwind freely from the spool and is not catching on:
- a notch in the reel;
- the spool cap;
- a thread guide;
- another spool or accessory; or
- anything else along the threading path.
It is also worth checking whether the thread suits the fabric and needle you are using.
You do not need anything exotic for ordinary sewing. A decent-quality all-purpose polyester thread is perfectly suitable for a great many everyday projects.
4. Check the Bobbin
Before blaming the upper tension, make sure the bobbin is behaving itself too.
Check that:
- it is the correct type and size of bobbin for your machine;
- the thread has been wound evenly onto it;
- it is not overfilled;
- it is sitting correctly in the bobbin case or drop-in bobbin area;
- the thread has been pulled through the correct guide or tension spring; and
- the bobbin has been inserted in the correct direction.
That last point is particularly important because sewing machines differ.
One machine may require the bobbin to unwind in one direction while another uses the opposite arrangement. This is one occasion when it really is worth looking at the threading diagram or checking your machine manual rather than relying on what your previous machine did.
Bobbins that look almost identical are not necessarily interchangeable either. A slightly different height or shape can be enough to cause problems.
5. Check for Lint and Loose Thread
Sewing machines collect fluff surprisingly quickly.
Lint can build up around the bobbin case, hook area and feed dogs, particularly when you have been sewing fabrics that shed a lot of fibres.
You do not need to dismantle the machine every time a stitch looks slightly odd, but it is worth checking for obvious lint and stray pieces of thread.
Clean the machine according to the instructions in your manual, particularly around the bobbin area if the manufacturer explains how to access it safely.
And the same applies to oiling. Some machines require sewing-machine oil in particular places and others are designed not to be routinely oiled by the user.
So don't automatically reach for the oil bottle either. Your manual gets the deciding vote on that one.
Why Am I Getting Loops of Thread Underneath the Fabric?
This is probably one of the most common sewing-machine problems to be blamed on bobbin tension.
You turn the fabric over and discover a tangled nest of thread underneath. Naturally, it looks as though something underneath the machine must have gone wrong.
But the cause can actually be the upper thread.
If the upper thread is not correctly seated in the tension system, the machine may feed far too much of it into each stitch. That excess thread can then collect underneath the fabric.
Before touching the bobbin tension or changing the upper tension dial:
- Remove the upper thread completely.
- Raise the presser foot.
- Rethread the machine from the beginning.
- Make sure the thread passes through the take-up lever.
- Check every thread guide.
- Rethread the needle correctly.
- Lower the presser foot before sewing.
- Test the machine on a scrap of fabric.
It may save you quite a lot of unnecessary fiddling.
If you’re getting a nest of thread underneath your fabric, How to Stop Thread Bunching Under the Fabric goes into the possible causes in more detail.Why Is the Bobbin Thread Showing on Top?
If you can clearly see the bobbin thread being pulled through to the top of the fabric, the balance between the upper and lower threads is not right.
That can be a sign that the upper tension is too tight, but again I would check the basics before changing anything.
Make sure the bobbin has been inserted correctly and that the bobbin thread is following its proper path. Check the upper threading as well.
If everything is correctly threaded and the problem remains consistent, then a small reduction in the upper tension may be appropriate.
Do Skipped Stitches Mean the Tension Is Wrong?
Not necessarily.
Skipped stitches are often more closely connected with the needle, fabric or threading than with the tension dial.
A damaged needle, an incorrectly fitted needle or the wrong type of needle for the fabric can all prevent stitches forming correctly.
This is particularly worth remembering with stretchy fabrics. If a machine sews woven cotton perfectly well but begins skipping stitches on jersey, changing the tension would not be my first response. I would check whether the needle is suitable for that fabric.
If skipped stitches continue with the correct new needle and correct threading, the machine may need further investigation.
Does Thread Breaking Mean I Need to Change the Tension?
Again, not automatically.
Very high upper tension can contribute to thread breakage, but so can:
- old or weak thread;
- thread catching on the spool;
- a damaged or unsuitable needle;
- incorrect threading;
- a burr or rough edge somewhere in the thread path; or
- using a needle and thread combination that does not work well together.
If the machine was previously sewing normally at the same tension setting, look for what else has changed before assuming the dial has suddenly developed opinions of its own.
So When Should I Actually Change the Sewing Machine Tension?
Once you have checked the threading, needle, thread, bobbin and obvious lint, and the stitching is still showing a consistent thread-balance problem, then it may be time to adjust the upper tension.
Tension may also need changing when you deliberately change what you are sewing.
For example, a different combination of:
- fabric thickness;
- number of fabric layers;
- thread weight;
- needle size; or
- specialist sewing technique
may require a slightly different tension setting from your machine's usual everyday setup.
The important word here is slightly.
Make small changes rather than swinging the tension dial from one extreme to the other.
How to Adjust Sewing Machine Tension
If you have reached the point where an adjustment is justified, work methodically.
- Make a note of the current tension setting.
- Prepare a scrap of the same fabric and number of layers as your project.
- Sew a test line using the same needle and thread.
- Change the upper tension by a small amount.
- Sew another test line.
- Compare the top and underside of the stitching.
- Continue with small adjustments until the threads meet neatly within the fabric.
Changing one thing at a time matters.
If you change the tension, needle, thread and stitch settings all at once, you may fix the problem but have absolutely no idea which change fixed it.
That is not especially helpful the next time it happens.
What Number Should Sewing Machine Tension Be Set At?
There is no single tension number that is correct for every sewing machine, fabric and thread combination.
Machines differ, and the numbers on the dial are settings for that particular tension system rather than a universal measurement.
If you are unsure about the normal starting position for your machine, check its manual.
From there, test on a scrap of your actual project fabric and judge the stitch itself rather than becoming too attached to a particular number on the dial.
Should I Adjust the Bobbin Tension?
For ordinary troubleshooting, I would be much more cautious about changing bobbin tension.
On many domestic sewing machines, routine tension adjustments are intended to be made using the upper tension control. The bobbin tension may already be set correctly for normal sewing.
If loops are appearing underneath the fabric, do not assume that means you need to tighten the bobbin tension. As we have already seen, that particular mess is often caused by an upper-threading problem.
If your machine manual gives specific instructions for adjusting bobbin tension for a particular purpose, follow those instructions. Otherwise, it is sensible to exhaust the normal threading, needle, thread and upper-tension checks first.
Testing Your Tension on Different Fabrics
A machine setting that produces lovely stitches on two layers of ordinary cotton may not behave identically when you move to something much heavier, lighter or stretchier.
That does not mean you should automatically adjust the tension every time you change fabric.
Start with the machine's normal settings, choose the correct needle and suitable thread, and sew a test seam on a scrap.
If the stitch balance is genuinely wrong after everything else has been checked, make a small tension adjustment and test again.
This is particularly useful before sewing an important visible seam. Discovering that your settings dislike your fabric is much less upsetting on a scrap than halfway down the front of the actual project.
Sewing Machine Tension Troubleshooting Guide
| Problem | What to Check First | Could It Be Tension? |
|---|---|---|
| Loops or thread nests underneath | Upper threading, presser foot position and take-up lever | Possibly, but incorrect upper threading is a common cause |
| Bobbin thread showing on top | Bobbin insertion and complete threading | Yes, upper tension may be too tight |
| Loose upper thread showing underneath | Upper threading and tension-disc engagement | Yes, upper tension may be too loose |
| Skipped stitches | Needle type, size, condition and insertion | Not usually the first thing to change |
| Thread keeps breaking | Thread quality, needle and threading path | Possibly, particularly if upper tension is excessive |
| Machine suddenly sews badly | Rethread everything and check the bobbin | Only after simpler causes have been ruled out |
When Should a Sewing Machine Be Checked Professionally?
If you have correctly threaded the machine, fitted a suitable new needle, checked the bobbin, tried good-quality thread, cleaned the accessible areas according to the manual and tested sensible tension adjustments without improving the stitch, the problem may not be something the tension dial can fix.
A machine that repeatedly skips stitches, breaks thread, jams or produces poor stitches despite correct setup may need servicing or repair.
Continuing to turn every available screw is not necessarily going to improve matters.
Sometimes the most useful troubleshooting decision is knowing when to stop troubleshooting.
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Frequently Asked Questions About Sewing Machine Tension
Should I change the tension if there are loops underneath my fabric?
Not straight away. Completely rethread the upper thread first with the presser foot raised. Make sure the thread passes correctly through the tension system, guides and take-up lever. Loops underneath can be caused by a problem with the upper threading rather than the bobbin tension.
Does a higher number mean tighter tension on a sewing machine?
On many machines, increasing the upper-tension setting increases the amount of tension applied to the upper thread. However, you should check your own sewing-machine manual rather than assuming every machine operates in exactly the same way.
Do I need to change tension for every fabric?
No. Start with your machine's normal settings and use an appropriate needle and thread. Test the stitching on a scrap of the actual fabric. Adjust the tension only if the stitch balance shows that an adjustment is needed.
Can the wrong needle look like a tension problem?
Yes. A blunt, bent, incorrectly fitted or unsuitable needle can produce skipped stitches, broken thread and generally poor sewing. Checking or replacing the needle is one of the simplest troubleshooting steps to try before changing the tension.
Why did my sewing machine tension suddenly go wrong?
If the machine was sewing correctly and suddenly starts producing poor stitches without you deliberately changing the settings, first suspect something simple. The upper thread may have come out of a guide, the thread may be catching, the needle may have become damaged or the bobbin may not be feeding correctly.
Should the upper and bobbin threads look identical?
The aim is a balanced stitch, with the two threads locking within the fabric rather than one being obviously pulled through to the opposite side. The exact appearance can vary with the fabric, thread colour and stitch being used, so test on your actual project fabric rather than judging the setting in isolation.
The Simple Rule
Before you change the tension on your sewing machine, check:
Threading. Needle. Thread. Bobbin. Lint.
If those are all correct and the upper and bobbin threads are still consistently being pulled out of balance, then start making small tension adjustments and testing each one on scrap fabric.
Tension absolutely can be the cause of poor stitching.
It just doesn't deserve the blame quite as often as it gets it.
And checking the simple things first can save you from creating a second problem while trying to fix the first.