Thread #, wt. or Tex – What Does It Mean?

What do those thread numbers on the end of the spool or cone mean and why should I care?  After reading this post, you will understand the different ways thread is numbered and how to choose the best thread for your project.

There are at least five different methods of measuring thread that provide information on the thickness of the thread and possibly its construction.

Wt. after a number refers to the weight of the thread.  The smaller the weight number, the heavier or thicker the thread.  A 30 wt. would be a heavier or thicker thread than a 50 wt. thread.

A # before the number is the Number Standard, a system developed in Japan known as the Gunze Count system.   As with weight (wt.), a smaller number also indicates a heavier thread.  Therefore, a #50 thread would be a heavier, thicker thread than a #70 thread.

Also commonly seen are two numbers, such as 50/3, which is the composition standard system.  The 50 in the same as a #50 thread and has 3 plies twisted together.  Although this system was originally developed for cotton thread, it has been adopted for plied polyester threads.

Two other methods of measuring thread are Denier and Tex which measure the actual weight in units of Denier or Tex of a standard length of thread.  With both of these systems the higher the number, the heavier the thread.  For example a 120 Tex would be a thicker thread than a 70 Tex thread because the standard length of the 120 Tex thread weighs more than the same length of a 70 Tex thread.

On the thread rack it will be common to see different brands or types of thread using any one of these measuring systems.  You will find #50 thread, 50 wt. thread, 50/3 thread, or even Tex 50.  Do not compare one 50 thread of one measuring system to another 50 in another measuring system.  They are not the same size or thickness.  When comparing threads it is important to compare using the same standard of measurement, such as wt. with wt., or # with #.

Understanding these numbering systems will help you choose the thickness you want for the type of project you are working on – sewing, embroidery, or quilting.  Remember, that the thicker the thread, the larger the machine needle you will need.  The eye of the needle and the groove to carry the thread increase as the size of the needle increases.  A #12 needle is smaller than a #14 or #16.  Use a #12 for thinner thread and a #16 for very thick thread.  On a longarm, use a #20 for thicker thread and a #18 for thinner thread.  (The reason is the high speed sewing)  Using the wrong needle size can result in skipped stitches and poor stitch quality.

Tips for thread choice:

  1. Decide what relative thickness you want for your thread based on the project.
  2. Choose the thread by comparing the numbers only in the same system.
  3. Based on the thickness of the thread, determine the needle size.
(some thread information courtesy of Superior Threads)


About Joyce Blowers

I am passionate about quilting - making quilts and quilting quilts. I started quilting about 30 years ago and over the years have taught sewing, heirloom sewing and quilting. I especially enjoy teaching new quilters the fundamentals of quilting that are so necessary to enjoying the art of quilting. As owner of Delightful Quilting & Sewing, a Nolting longarm dealership in New York State, I also enjoy helping new longarm quilting machine owners become confident longarm quilters.
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