What is Thread Weight

Different threads on a bathroom scale
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Thread Weight

I swear, sewing comes with its own special language and a lot of it doesn’t even seem to be based on logic. I’m starting with some basics and decided to learn more about thread. Thread weight, to be precise. LOL, and as I am frequently discovering, not as simple a topic as I first thought.


What is Thread Weight?

Thread weight is what many sewers think of when they think of thread size. It’s actually one of numerous sizing labels that can appear on your spool of thread. I always assumed the different pre-fixes (wt, #, Ne, No, Tex) were all thread weight, just the different ways manufacturers liked to write it.Different thread size labels

Nope. Turns out some of those labels are a different measurement that uses a different formula. Hee-Haw. Now that I think more about it, it was like assuming a spool labeled 300m (for meters) would be the same length as a 300y (yard) one. 

For this post, I’m going to focus on thread weight. If you’re interested, there are charts out there that show you how to convert between the different measurement systems. If you’d prefer to bypass all that, I created a Thread Thickness Cheat Sheet that lists many popular threads from thinnest to thickest next to their labeled sizes.

If you’d like to learn more about the different types of measurement the thread industry uses, the most helpful article I found was this one: Unraveling the mystery of thread size by Ken Nelson, a Product Manger at Coats & Clark.

How is Thread Weight Measured?

How thread weight is measured.

Let’s just start with this, thread weight is counter intuitive. The heavier the thread the smaller the number/thread weight. Basically, thread weight is how much length of a thread it would take to reach a certain weight. To be exact, how many meters of a particular thread it would take to weigh 1 gram. (For us metrically challenged folks, 1 gram is equal to 0.035 oz.)

If you look at the graphic of the balance scale, it takes 50 meters to weigh 1 gram. So That thread would be considered a 50 Weight Thread.

A thicker heavier thread would only take 20 meters and a fine thread might take 200 meters to reach the same weight of 1 gram.

(Quick note, I also saw the formula written as “How many kilometers to equal one kilogram.” It gives the same results but would be a lot harder to measure. One kilometer is over half a mile of thread.)

Thread Ply

Three ply sewing threadNow, there is sometimes a number right after the weight (50/3) and that refers to how many ply make up a single strand. Ply are just the individual sections you see pulling apart at the end of your thread. I’ve unraveled a 3 ply thread here to show you.


Another level of complexity

Visually see the difference between cotton and polyester

So, one last major thing I noticed. It doesn’t matter what measurement system is used, different thread fibers shouldn’t be compared willy nilly to one another. Different fibers have different physical weights. Take a look at these two threads. Both are No 40 but one is Polyester and the other is Cotton. You can see that polyester is thinner, even though they are both sized at a No 40.


So why does it matter?

Matching thread size to needle size

The weight/size of your thread is usually your first clue to what size needle to use. You will have a happier time sewing if your thread and needle fit well. If the thread is too thick (low thread weight) for the needle’s eye, you can have shredding, skipped stitches or other issues. Threaded Needle close up

Some thread manufacturers (Superior Threads) list their recommended needle size right on the spool, but most don’t. Most do have it listed somewhere on their website, but it can be tricky tracking down.

I hate not going further into this, but matching thread and needle sizes is something I want to do more research on a later post.


Thread in bobbinThread weight/thickness also effects your tension. When you set your tension, you are setting an amount of space for the thread to squeeze through (the tension disks).

If your tension is set for a thinner thread and you switch to a thicker thread, you’re now trying to pull the thread through a gap that is a little too small. This is why your tension sometimes needs to be adjusted when you change threads. A lot of computerized machines have some form of auto tension adjustment that helps, but manual machines don’t and will need to be tweaked more often.

This picture is just a visual aid. I slid the threads into the bobbin half way so I could show the threads moving tension mechanisms apart. I couldn’t easily get to my upper tension disks in my sewing machine. This is the bobbin spring in my bobbin case. If you look closely, you can see there is more space next to the thicker orange thread. The thinner thread on the left kept falling out of the bobbin when I was trying to take this picture. It was because the bobbin spring was already spread so wide from the thicker thread.

Visual Effect

A size Ne50 and Ne12 thread stitch side by sidePeople also use different thread weights/thicknesses for different effects on their quilts.

You can look for a lower thread weight (thicker thread) to make your quilting really stand out on top of a quilt. This is great for details you really want to stand out.

A higher thread weight (thicker thread) will blend into the background more. You can match thread color to the fabric to make it disappear against the quilt.

Seam Thickness

Measuring pressed seamsA higher thread weight (thinner thread) can be good for making seams lay flatter. A physically smaller thread makes less bulk, but I’d keep the strength of your seams in mind. Thinner threads are often weaker. Sounds like another experiment.

orange dotted lines with nosy quilter logo in the middle

Next time

While I learned a lot from researching this post about Thread Weight, I really do want an easier way of comparing thread sizes. I am particularly interested in thread thickness. 

I’ve picked up 26 different spools of thread to run a thread thickness experiment. My thread samples come from big box stores, online and my local quilt shops. I wanted to cover threads in a variety of price ranges. I did my best to get different sizes and fibers. I hope you’ll join me next time as I do a physical review on thread thickness between brands and fibers.

Sew Curious, Evie


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3 thoughts on “What is Thread Weight

  1. An attention-grabbing dialogue is worth comment. I feel that you must write more on this matter, it might not be a taboo subject but usually individuals are not enough to speak on such topics. To the next. Cheers

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