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Understanding Thread Weight

The weight or size of thread is an important consideration for any sewing project. Making proper adjustments relative to different thread weights will make sewing, quilting, or embroidery projects more enjoyable. The five most common methods of measurement of threads are weight, denier, tex, number, and composition standards.


A smaller weight number indicates a heavier thread. The weight of a thread is actually a length measurement. Dividing the length of thread by a set weight derives the exact measurement of a thread weight. A thread is labeled 40 wt. when 40 kilometers of that thread weighs 1 kilogram. A 30 wt. thread is heavier because it takes only 30 kilometers of thread to weigh one kilogram.


Weight in grams of 9000 meters of thread. If 9,000 meters weighs 120 grams, it is a 120-denier thread. Many polyester and rayon embroidery threads are 120/2, which equals 2 strands of 120-denier thread for a 240 denier total. Larger denier numbers are heavier threads.


Weight in grams of 1000 meters of thread. If 1,000 meters weighs 25 grams, it is a tex 25. Larger tex numbers are heavier threads.

Number System

The Number standard is used on many thinner threads and is written as No. 50 (or #50) or No. 100 (or #100). Many people confuse this with a Weight measurement and incorrectly suppose a No. 100 thread is a 100 weight thread. The Number standard was developed in Japan and is known as the Gunze Count system. The smaller the number, the heavier the thread. It is not necessary to know the exact conversion formula. Just remember that a spool of thread stamped with No. 100 does not mean it is a 100 weight thread. One spool of thread may be stamped No. 50, another spool may be stamped 50 wt., and yet another spool of thread may be stamped 50/3. All three of these are measured using different standards and we must not assume they are similar in size. When comparing threads, make sure you use a consistent standard of measurement and the best reference is your eyes and fingers to gauge the diameter of thread.

Composition standard

The composition standard was developed for cotton thread but has also been adopted for polyester threads. A cotton thread and a polyester thread with identical Composition numbers will be similar, but not exactly the same size. This is because we are comparing apples to oranges. For exactness, it is always necessary to compare cotton to cotton and poly to poly. This standard uses numbers like 30/3 (or 30/1x3) and 50/3 (or 50/1x3). For heavier threads, the first number represents the same number used in the Number Standard and the second number represents the number of plies of thread twisted together. For example, a 30/3 means the thread is a 3-ply No. 30 thread. Most thin threads (50 wt. and thinner) are a 2-ply thread. Most heavy threads are a 3-ply thread.

Thread Weight

The thicker the thread, the smaller the number (top thread is 100 wt. and bottom thread is a 12 wt.)

  • A basic conversion chart for understanding thread measurements:
  • Weight to Denier 9000/weight
  • Weight to Tex 1000/weight
  • Denier to Weight 9000/denier
  • Denier to Tex denier x 0.111
  • Tex to Denier tex x 9
  • Tex to Weight 1000/tex
  • 40 weight = 225 denier = Tex 25

The importance of thread weight

The weight of thread influences several aspects of a quilt, article of clothing, embroidery design, or craft. Stitch density, area, or field density, needle size, and tension.projects, mainly field densities, needle size and tension.

Stitch and field density

Most digitized designs are created for 40 weight thread. This ensures adequate coverage for embroidery. If a 30 weight thread is used, the increased diameter of the thread can present a lumpy appearance or cause the thread to bind on itself which will break the thread or jam the machine. To correct this, reduce the density by one-third or increase the design size by 125% of the original. Increasing the stitch length will also help.

Needle Size

A general rule is to use a needle whose eye is 40% larger than the diameter of the thread. If you use a #75/11 or #80/12 size needle for 50 weight thread, you should use a needle with a larger eye when sewing with a heavier thread. We recommend a size #90/14 when sewing with a 40 wt. thread and a #100/16 needle when sewing with a 30 wt or 12 wt. thread. If you find your thread to be shredding or skipping stitches, try a new needle and go up one size.


Thread tension on most sewing machines is accomplished by applying pressure to one side of a spring that presses on a tension disk. Tension is applied to the thread as it passes between a pair of tension disks. Tension may be adjusted mechanically by means of a thumb wheel, or electronically through a computer-controlled electromagnet. Increased pressure on the tension spring increases thread tension. When a 40 wt. thread is replaced by a heavier 30 wt. thread, the increased diameter pushes the tension disks further apart, increasing pressure on the tension spring. Just by increasing (or decreasing) the diameter of our thread, we have increased or decreased the thread tension. If the tension is too high, it damages the thread and the thread can break. If it is too low, the thread will loop on the back of the fabric. When you change threads, remember to take the diameter of the new thread into consideration and make adjustments as necessary.


In summary, the most common method used to gauge the diameter of threads today is the weight system. While the weight system is not an exact science, as accounting for the number of plies is usually discarded, it is recognized as being the most popular for quilters and sewists alike. To gauge how a thread will look when stitched is to take the thread in your hand, pass it between your fingers, lay it over your fabric, and see how it looks. Once you have a favorite or go-to thread that you commonly use, this thread should be your benchmark when comparing different threads.

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