Serger Tension Made Easy

A serger is a fantastic sewing tool that I highly recommend to any sewist that can afford one. This is especially true if you like to sew with knits (see why in my post In Praise of Sergers). But many sewists shy away from them because of the ongoing frustration of perfecting the serger tension.

Welp. That’s precisely why I decided to write this post. Serger tension can be tricky for the beginner sewist. But with a little bit of clarity, you’ll know exactly how to turn those dials or knobs to achieve the perfect tension for all of your sewing projects.

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So let’s get started! To help guide you through understanding the tension on your serger, I’m pulling out my handy tension swatches.

I am using my Juki-MO654DE (p.s. If you’re shopping for a serger, this baby is my number one recommendation. It is the absolute best bang for your buck. Mine is over 15 years old and I swear has another 15 or more years to go.)

For the sake of this tutorial, I used some pretty psychedelic thread colors. In my lower looper – fuschia, upper looper – sky blue, right needle – black and left needle – neon purple.

Now depending on your serger, you will either be working with a set of knobs or a set of dials to adjust your tension. The numbers will also be unique to your particular make and model. My Juki uses a knob system with each on a scale from 1–9.

As you can imagine the higher the number the higher the tension.

Editor’s Note: Enjoying this sewing tutorial? Put it to use on our Nora Sweater!

But what exactly does tension mean?

Higher tension means there is more friction on the thread as it is being pulled through the machine. More friction means the thread will be sewn in tighter. Perfecting your tension means creating a perfect balance of “tightness” between all of the threads.

Imagine a teeny tiny game of tug of war between the threads. When the fabric is perfectly settled between all threads, you’ve got yourself a balanced stitch. With a two needle serger, this means four threads.

Let’s Begin with a Balanced Stitch

The two pictures below are of a perfectly balanced stitch.

You’ll notice that the two looper threads (the blue and the fuschia) meet right at the fabric’s edge. There is also no puckering at the needle threads (black and purple).

Now let’s take a look at some unbalanced examples.

Troubleshooting Unbalanced Loopers

Let’s start with the loopers. In this first example, we are looking at the upper looper thread (blue) being set with too much tension. Notice how it is so tight that it is pulling down on the lower looper thread (fuschia) which is causing the fabric to “tunnel”. You’ll also notice that since it is pulling down on the lower looper thread (fuschia), the lower looper thread is now pulling up on the left needle thread (purple).

This second example is with the upper looper thread (blue) being set with too low of tension. In this case, there is no resistance against the lower looper thread (fuschia) which is making it loose and wavy on the backside of the stitch.

Next, let’s check out our lower looper settings. In this next picture, we are looking at the lower looper thread (fuschia) with too much tension. Similarly to the high upper looper example, the lower looper thread (fuschia) is pulling down on the upper looper thread (blue). Also notice how its tightness is also pulling up the left needle thread (purple).

In the case of the lower looper thread tension being set too low, you will see the lower looper thread (fuschia) being carried over to the front side of the stitch by the upper looper thread (blue).

Now Onto Needle Tension

Needle tension isn’t quite as finicky as looper tension, but it is still just as important. Let’s start with the right.

This first example is when your right needle thread (black) tension is set too high. There are two signs of your tension being too high. First, you’ll notice some puckering at the stitch line. My swatches are sewn with a super stiff muslin material, but if you are sewing with a lighter woven or knit, you will see this straight away. Another thing to notice is how the right needle thread (black) is so tight that it is pulling the lower looper thread (fuschia) through the fabric onto the front side.

Now if the right needle thread (black) tension is set too low, like in the following picture, you will see the right needle thread (black) hanging out loosely on the front of the stitch and create loops on the backside of the stitch.

Lastly, let’s look at the left needle. The following picture shows the left needle thread (purple) with too much tension on it. Just like the right needle, when the left needle thread (purple) is too tight it will pucker and pull the lower looper thread (fuschia) through to the front of the stitch. Notice how tiny the left needle stitch (purple) is on the backside of the stitch. It’s so tight you could barely pick it if you had to!

Now if the left needle thread (purple) tension is set too low you will instantly know because it will be showing through on the right side of your garment. If you’ve ever sewn something with negative ease and put it on only to see your thread showing on your seams, your left needle thread tension is too low. Just like the loose right needle thread, if the left needle thread (purple) is too loose, you will see loose stitches on the front of the stitch and little loops on the backside of your stitch.

Bird’s Eye View

I know it can be easy to get lost in all of these examples so here’s a comparison chart for you to see them all together:

Adjusting Tension for Different Fabrics and Thread Types

Now as much as it may stress you out, you will absolutely have to change your tension settings as your fabric choice and thread choices change for each project. The tension was put on dials and knobs for a reason – so you can adjust them! Serging denim is going to have different settings than serging sweater knit. Thin polyester thread will need different tension than fluffy wooly nylon.

More often than not, however, you will end up cycling through similar fabrics, threads, and settings. Which is why it’s nice to have these things on hand so you don’t have to fiddle with your tension every time you switch things up.

I like to keep mine written down on these printable cards. Simply describe what the settings are good for then write down the appropriate tension for each dial. There is also a spot to write in your differential feed.


Ready to start serging?? Good! I hope this was helpful and feel free to leave any questions or comment below.

39 thoughts on “Serger Tension Made Easy”

    1. I have a toyota serget
      Can you tell me the best settings for this machine. In addition, do you always have to use two needles and which needles do you use for bezt results. Thanks
      Joyce, south london

      1. Hi Joyce! I don’t own a Toyota serger so unfortunately I can’t be very helpful for information on that specific machine. The best thing I could recommend is reading through the manual. If you don’t have a physical version, almost all machine manuals are now available online for you to reference. As for needles – you will want to use a different type of needle depending on the fabric you are working with. You can find more information about that here: The size of needle you will want to use should also be mentioned in your machine’s manual. I hope that is helpful!

  1. I have watched numerous videos, read countless tutorials on serging. This, however, has been the absolute best! Thank you so much for taking some of the frustration out of getting my tensions right on my new serger.

  2. Thank you for this. I just got my first serger and was struggling to get a clear understanding of what a balanced stitch looks like. This was perfect!! I’m ready for my first project now 🙂

    1. Thank you, thank you, thank you! I was doing my nut trying to find the cause of the loops on the lower thread. I also have the same Juki model as you and was frightened of it for two years but I’m now loving it and making loads of curtains and blinds for our new home! You have saved this latest frustration turning into a complete disaster 🙂 and I will definitely recommend you and return for more!

  3. There are not enough words for “angry” to tell you how mad I am at this stupid serger!!! I have the Juki MO-644D. It worked GREAT until I re-threaded it for my next project. Now, the tension is all messed up. I’ve tried all of your solutions (Thank you for the illustrations– so much more helpful than drawings!!) and I can’t get it to work. I re-threaded it with 4 different colors of thread, and I’ve narrowed it down to the left-side needle. I took the needle off, and the stitches look better, but, I want to be able to use all 4 threads!! I guess I’ll have to make another trip to the sewing store… argh.

    1. How long has it been since your last service? Sometimes the devil starts playing in there and a good servicing is the only fix. Especially if it’s been a while.

  4. I’m still not any closer to figuring out what I’m doing wrong. I’ve been using this serger for 20+ years and have never had the tension messed up like it is now.

  5. After I’m done serging two fabrics together for a seam, i flip it so the right sides are facing out, you can easily see the thread joining the two pieces together (sewing knits, making a hoodie) I’d assume my left needles tension would need to be higher to make the stitch tighter, but that doesn’t help. Any suggestions?

  6. Can you share your settings for different fabrics so I have a baseline. I’m going nuts trying to figure out my tensions and differential feeds and Stritch length on thinner fabric (RS, modal, bulgaree, etc)

    1. Thinner fabrics can be trickier. I like to widen and lengthen my stitch for those fabrics since they have a harder time feeding through. You can also increase your seam allowances if you are using a narrow seam allowance and it is folding up next to the knife rather than getting trimmed. When all else fails, if lighter fabrics are misbehaving you can use a wash away stabilizer. As far as a baseline goes, it really depends on the machine 🙁 My Juki is over 20 years old so her settings are far from typical. Most brands will have you start at 4-4-4-4 then adjust from there. I would try to get everything nailed down on some starched cotton, then starting working your way over to the thinner stuff. I hope that is helpful!

  7. I have the same problem – my “solution” is to sew a seamline outside the serger stitch with my sewing machine.

  8. Wow! I finally understand what my serger actually does… thanks! I think you just saved the troublesome relationship we had going on, my serger and I might still become friends

  9. Thank you for your tutorial. It walked me through and held my hand. Now I know my left needle tension is non-existent and my poor baby needs to go see a qualified technician.

  10. Thank you so much for your very easy to understand video. I have brother 4234D in beginning it was fine, but when you try different stitch style like rolled hem , 1 needle 3 threads overlock i needed to change the setting accordingly. After long struggled I have to decide rethread every time I change stitch style and change tension settings little at a time and works fine. I am taking advise from you and seeing all the picture made me to use my overlocker even m ore now.

    So thank you so much for very informative information.

    Also thank you for “SERGER SETTING CARDS” made my life even more better.

  11. Wow, this is a HUGE help for me. A friend just gifted me her old Bernina serger. I am a sewer of many years, but I have never owned a serger, or even been around one, before. I am overwhelmed especially by the threading sequences (I just need to practice) and tension. You have really helped me with the tension. I printed your chart and your cards. Thank you so, so much!

  12. You’ve given me courage to approach my serger. It has more needles and cones, but this tutorial is a great place to start. Thank you!

  13. I cannot figure out why my threads are looping on the back side of the fabric, rather than just showing as straight stitches – any ideas would be helpful! Thanks! I also have the same Juki as in your display.

  14. Eve Jones–sometimes I found that tracing the thread from the cone all the way through to under the presser foot helps me to find a spot where the thread wasn’t where it was supposed to be on its path. That can affect tension, also. Good luck!

  15. I tape a sample on index cards of the front and back of the serged fabric with the settings that worked for that fabric. Sometimes I include samples of settings that did not work with the explanation — once I figure it out. I do this for each project. However, keep in mind these settings may work great for a light weight knit but not baby flannel or other fabrics.

    I recently had an epic serger fail. I bought a new Serger several weeks ago. The chaining kept failing. Panic set in. I re-threaded multiple times. Still nothing. Finally, I realized there was one step I had not redone. I checked the needle position to see if it was all the way up in the needle holder. It was not. Problem solved. It also could have been in the wrong needle slot but in this instance it was ok.

    If your chaining is looking really terrible after repeated adjustments as clearly presented by the author, or if they are not forming at all not, I recommend cutting alI threads and and take out your needles. Check the feed dog for tangled threads and/or fabric. Redo the serger setup in the order provided in the users manual. This will solve most problems.

    Happy serving.

  16. Christopher M. Lee

    Thank you!
    This is the most informative explanation I have found. After hours of piddling around on other media. I was up and running like a pro in less than 5 minutes!

  17. Thank you so much for this post! It saved me a lot of time troubleshooting my serger stitching (Low right needle tension, low upper looper tension :))
    Pinned it for the next time I change up my fabric/thread.

  18. Terry Ann Crofts

    Thank goodness I found your website! One quick question though, when using woolly nylon (in both loopers) would you normally increase or decrease the tension? I just can’t seem to get it right! I am trying to make myself some short leggings for running (polyester/lycra sportswear fabric).

    1. Hi there! It honestly depends on the machine you are using. I have found that I can maintain the same tension for my particular machine. I would set aside some time to play with it. Start with regular polyester thread on 100% cotton fabric. Then switch to your wooly nylon and see what kinds of adjustments you had to make. With cotton being one of the least fussy fabrics to work with, it can make identifying thread adjustments easier. Then you can apply the same concepts to your standard knit fabric tension settings. 🙂

  19. Thank you, thank you! I was going to try and make a DIBBY Tee yesterday but realized I need to take an extra day an learn to adjust my serger. My knit is really light, and probably too difficult a fabric for a novice but I’m going to try all your steps. I want to get good at the serger so its worth taking a day. Thanks again.

  20. I also have a Juki serger that I love. I love Juki so much I have them in straight stitch, serger, and regular sewing machine. But, I have to say that the information you have given us here is SO much better explained and presented than the owner’s manual. THANK YOU for putting this together and offering it!

  21. This is the best serger tension tutorial I’ve seen! I’ve pinned your site in my Pinterest MONTHS ago, and this is the first time I’ve taken the time to actually read your post! I have the same serger, I am excited to just go sit down and hopefully tackle tension! AND….the printable…..fantastic!

  22. Kimberly Whitfield

    Ok. My problem is that I have a little wave pattern. I have adjusted up and down but ai still get this little wave. I am not sure what is happening. Not a wavy edge but a wave in the stitches. Here is the best way I can describe it without a photo: perfect overlock, then LL waves over front of fabric for three or four stitches, on the back it looks like the Left needle is low in some spots where this happens, then back to fine overlocking UL AND LL. Ugg. I am using a Double layer of thinner inexpensive muslin. No pucker issues just uneven UL and LL. I tried adjusting the tension up and down but it makes it worse not really better. Any ideas? Stitch width 2 DIF set at N knife set at 1.

  23. Astonishing! I have four different coloured threads to troubleshoot. Then I read a comment about cleaning out the tension discs using dental floss. Did this, and immediately got perfect tension !! Must have been something stuck in there I couldn’t see and never would have found. Thank you thank you thank you!

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