A little about Thread Weight Measurements

Finding the right kind of thread for your project can be daunting! There are so many different types: different materials, weights, and shine.

There is too much about thread to write about all at once, so I will start with: thread weight measurements.

There are three common thread weight measurements that you may see in the industry. These are: Weight (W or wt), Denier, and Tex. Each of these is different and you need a conversion chart to convert from one to another.

A spool of 40W or 40 wt. thread

The one I am most familiar with and use is Weight (W). Common thread weights are 12W, 28W, 40W, 50W, 80W, and 100W, although there are others. The lower the number, the heavier weight the thread is. These measurements are determined by the number of kilometers (km) of thread that it would take to weigh 1 kilograms (kg). So it takes 12 km of 12W thread to weigh 1 kg, while 100 km of 100W are needed to weigh 1 kg. In other words, since the 12W is thicker you need less thread to reach 1 kg, whereas the 100W is very thin and so it takes more thread to reach 1 kg.

Denier is often used by flyfishers for tying flies. But it can be used in sewing as well. Denier threads tend to be polyester or nylon. The measurement is determined by how many grams (g) of thread it takes to measure 9,000 meters (m) of thread. Some common weights you will see in deniers are: denier 70, denier 140, denier 210, and denier 280. So for denier 70 it takes 70g of thread to measure 9,000 m, whereas it takes 4 times the amount of denier 280 to measure 9,000 m. The lower the denier number, the thicker the thread. (I don’t have any Denier in my studio.)

The last common measurement of thread is Tex. Kevlar and Halo threads use Tex, as do some fusible threads, as some examples. Tex is found by determining how many grams of thread are in 1,000 meters (m). The higher the tex number, the thicker the thread. This monofilament thread I have in my studio is measured in Tex. It is Tex-15.

This Coats Transparent thread is Tex15. I looked it up online by inputting “Coats Transparent thread 29650”

This spool reads “No. 50” - not to be confused with 50W (or 50 wt.).

Unfortunately, the weights and measurements for thread are not standardized. Different companies measure their thread differently yet may still use the same notation as another company does. However, the notations don't necessarily mean the same thing across all companies. Also, thread measurements can differ in different countries. For example, the Number System is a Japanese notation for thread. You might see No. 50 or #50 on a spool, but it does not mean that it is the same as 50-wt or 50W.

Some companies don’t put their weights and measurements on their labels. So what do you do? My advice is to look up the company online and input the numbers on the label. You should be able to find information for that spool. Write the weight on the spool using a marker and even keep track of it in a notebook.

Once you understand these basics, it is easier to play around with various threads and learn from your own experiences! Sometimes you can “eyeball” the weight of a thread if you have a control (one that you already know the weight of) or as you gain experience working with different thread weights.