Understanding Thread Tension

One of the most tricky parts of sewing - whether you're a beginner or experienced sewist - is understanding thread tension. While it is needed to adjust thread tension if you're switching between different thread, needle or fabric thickness, very often this setting is left untouched. And too bad, because fine-tuning thread tension is a must to create a strong, durable, well-balanced seam!

In this article, I want to share one very helpful experiment, that will help understand thread tension better. This experiment will take just a few minutes, so grab your sewing machine and follow along!

Before we start the experiment, I want to thank Mettler for partnering on this post. I've been sewing with Mettler threads for the past 5 years and their product quality speaks for itself. In this experiment, I'll be using one of my go-to thread choices - Mettler METROSENE, an all-purpose sewing thread that comes in over 300 colors. Click here to explore entire Mettler thread range.

Threads used in this post - Mettler METROSENE all-purpose sewing thread

Understanding Thread Tension

STEP 1: prepare sewing machine.

For thread tension experiment, let's prepare the machine by threading it with same thread, but in contrasting colors: for the top, I'll use Mettler METROSENE teal colored thread, for the bobbin - red color Mettler METROSENE thread. Having same thread will allow to properly balance top and bottom seam, while contrasting color will reveal where seam disbalance happens.

Thread machine with same type thread, using contrasting colors for top and bottom

STEP 2: testing tension setting '0'.

After threading sewing machine, lower the presser foot to engage top thread tension.

On thread tension disc, select tension '0' - lowest tension setting. Try to pull the top thread and you can see how easy it is to pull, as top thread has no tension (aka, the tension is set on zero).

With tension set on '0', with lowered presser foot, top thread is easy to pull due to no tension

Now with your sewing machine set on tension '0', sew a seam. What you'll see is that top thread does not lay flat on the fabric, and it forms top thread loops on the fabric bottom - this is an indication that thread tension for this fabric, needle and thread is too low, and the seam is not balanced.

Tension '0' seam top view

Tension '0' seam bottom view

STEP 3: testing tension setting '9'.

Now let's do a reverse test: lower the presser foot again and now on thread tension disc, select tension '9' - highest tension setting. Try to pull the top thread and you can see how hard it is to pull, as top thread has lots tension (aka, the tension is set on max).

With tension set on '9', with lowered presser foot, top thread is hard to pull due to high tension

With your sewing machine set on tension '9', sew a seam. The top thread is now so tense, that it pulls bobbin thread loops to the right side of the fabric - this is an indication that thread tension for this fabric, needle and thread is too high, and the seam is not balanced.

Tension '9' seam top view (bottom seam)

Tension '9' seam bottom view (bottom seam)

STEP 4: testing tension setting '4'.

For final part of the test, let's lower the presser foot again and now on thread tension disc, select tension '4' - medium tension setting (typically, on your sewing machine thread tension disc there will be a marking, showing which setting is 'medium' - on my machine, this range is between 3-5. Medium tension setting is suitable to sew most medium weight woven fabrics with all-purpose sewing thread and size 90 needle). Try to pull the top thread and you can see that it pulls rather easily, though has more resistance than with no tension.

With tension set on '4', with lowered presser foot, top thread is rather easy to pull, though has some resistance

Sew a seam with tension '4'. The top thread now lays flat on fabric, there are no big loops on top or bottom of the fabric - this is an indication that thread tension for this fabric, needle and thread is correct, and the seam is balanced.

Tension '4' seam top view (bottom seam)

Tension '4' seam bottom view (bottom seam)

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This is it, out thread tension experiment is completed! I hope that these 4 easy steps will bring better understanding how to use thread tension and fine tune it for perfect seam results! To watch video version of this test (along with 4 extra sewing tips!), click screen below:

Best wishes,

Julija Gobere

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