Thread Sizing Guide

Thread Size Measurement: Two primary methods, length and weight.

Weight — In weight measurements, higher numbers reflect finer or lighter threads. The “weight” of a particular type of thread refers to the length of a given weight of thread. Dividing the length of thread by a set weight derives the exact measurement of a thread weight. A thread is labeled 40 wt. because one gram is 40 meters long. A thread is labeled 30 wt. because one gram is 30 meters long. A 30-wt. thread is a “heavier” thread, meaning a thicker cross section, because a much shorter thread weighs the same as the 40 wt.

Length — in length measurements, higher numbers reflect thicker or heavier threads. “Denier” refers to the weight in grams of 9000 meters of thread. If 9000 meters weighs 1120 grams, it is a 120 d thread. Most embroidery threads are 120/2, which equals 2 strands of 120-denier thread for a 240 denier total.

“Tex” refers to the weight in grams of 1000 meters of thread. If 1000 meters weighs 25 grams, it is Tex 25.

Rule of Thumb — 40 Wt. = 240 denier = Tex 25. All work in a size 75/11 needle. SCHMETZ advises that the diameter of the eye of the needle should be 40% larger than the diameter of the thread. Using the rule of thumb, consider a larger needle when using threads heavier than 40wt/240denier/tex25. Consider using a smaller needle when using finer threads.

Conversion Factors


The Physical Dimension of a Thread Affects:

  • Both top and bobbin tensions — Changing the thread physically changes the tension. When thread size is changed, the upper and lower tensions should be checked.
  • Thread displacement — Too many thread fibers in a set space make the fabric pucker. Reduce field density, scale pattern or increase stitch length.
  • Needle selection — Eye of the needle should be 40% larger than the diameter of the thread. When going to a larger size thread, a larger needle should be used.