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Determine the Diameter (Thickness) and Width of the Sewing Thread

Thickness (or diameter) is one of the basic physical properties of industry sewing threads. The thickness and the diameter of a sewing thread refer to the same property that determines the size of the thread. It is the measure of the cross-sectional area of the thread, commonly expressed in millimeters or inches. The diameter or thickness measurement is essential for determining the right needle size, tension, and stitch length to use when sewing with a particular thread. The thicker the thread, the larger the needle size and stitch length required.

Therefore, knowing the diameter or thickness of a sewing thread is crucial for achieving the desired stitch quality and appearance on your fabric.

Thickness and width of the sewing thread

Bulk and warmth properties of textile materials are often estimated from their thickness values, and thickness is also useful in measuring some performance characteristics, such as before and after abrasion and shrinkage.

Not to be confused with thickness, the width of a yarn or tape is also a very important measurement. The width of a material helps to determine how much yarn coverage there will be when a material is laid flat on another surface. Width is an important factor when determining the coverage of yarn in a bundled cable, determining the needed pitch for a braided or spirally wrapped hose, or when calculating pore size and fabric density in woven fabrics. These methods cover the determination of the thickness and width of the tape, monofilament, multifilament, and spun yarns, either single or cabled, natural or colored.

Use tools to determine the sewing thread diameter and width

Polyester Filament Sewing Thread
Polyester Filament Sewing Thread

To determine the diameter (thickness) of a thread, you can use a micrometer or caliper, which are tools that measure very small distances. Place the thread between the jaws of the tool and gently close them to get the measurement. Be sure to measure in several places along the length of the thread to get an accurate average thickness.

To determine the width or “size” of a thread, you can use a thread gauge or comparator, which is a tool that has a series of different-sized slots that are labeled with corresponding numbers. Simply slide the thread through each slot, starting with the smallest, until you find the slot that the thread fits into snugly. The number labeled on that slot corresponds to the thread size.

Bear in mind that thread size is not directly related to thread thickness or diameter. Thread size is more commonly used in the context of machine sewing or embroidery, and is often given as a number (e.g. 50, 30, or 12), rather than a measurement in inches or millimeters. The higher the number, the finer the thread; the lower the number, the thicker or heavier the thread.

Steps of Test Procedure for Measuring the Diameter of Yarn and Thread

Tools Needed: Digital Thickness Gauge with 10mm diameter presser foot/feeler

4 steps

  • Cut four short 3” length samples of material and lay them parallel to each other on the presser foot. Materials should be spaced closely to minimize compression and spread of the fibers which can result in a less accurate measurement
  • Lower the feeler/presser foot onto the material being measured
  • Raise and lower the presser foot three times onto the sample and record the measurement
  • Average the results from the 3 readings

Procedure for Measuring the Width of Yarns and Tapes

  • Tools Needed: Digital Calipers
  • Requirements: The material will be measured in a pre-tensioned state to determine the accurate width


  • Determine pre-tension weight to be used – typically 0.05 grams per denier
    • e.g. for 1000 denier = 1000 x 0.05 = 50 g;
  • Cut three 18” samples of material to be tested;
  • Place one end of the material in a stationary clamp and the other end of the material over a roller or fixed bar;
  • Tension material by attaching determined pretension weight to end over the roll, making sure it is suspended in air;
  • Zero out calipers and carefully set the fixed end on edge of the material while carefully moving the adjustable end against another edge of the material,
  • Record 3 measurements at least 1.0” apart;
  • Repeat steps 3 – 6 for the remaining 2 samples, and
  • Average results from 3 samples.

Works Cited: How to Determine the Diameter (Thickness) and Width of Yarn or Thread