Embroidery Thread Weight Converter

Embroidery thread weight is described using several different numbering systems that can be confusing because some use direct counting and others use indirect counting.

Direct systems (higher number = heavier thread):

• Denier (D): The weight in grams of 9,000 meters of thread. A 120-denier thread means 9,000 meters weighs 120 grams.
• Tex: The weight in grams of 1,000 meters of thread. A 40-tex thread means 1,000 meters weighs 40 grams.
• Dtex (decitex): The weight in grams of 10,000 meters of thread. This is simply tex multiplied by 10.

Indirect systems (higher number = lighter thread):

• Weight number (Wt): Common in embroidery. A 40-weight thread is finer than a 12-weight thread. This roughly corresponds to the number of kilometers of thread that weigh 1 kg when using a single ply.

Conversion formulas using tex as the base:

• Tex = Denier / 9
• Denier = Tex x 9
• Dtex = Tex x 10
• Tex from Wt (approximate) = 1000 / Wt (for single-ply cotton-type threads)

Common embroidery thread weights:

Stranded floss, and why it does not have a weight number

Six-strand cotton floss is sold by strand count, not by a weight number, which is why it never appears in the table above. The arithmetic still works, because tex is additive: put two strands together and you have twice the tex. So a bundle of n strands of a thread measuring T tex comes to n × T tex, and because the weight number is the reciprocal scale, the bundle’s effective weight number is the single strand’s number divided by n.

That gives a rule worth remembering: doubling the strands halves the weight number. Two strands of a 60-weight thread behave like one 30-weight thread. Three strands of the same behave like a 20. The strand-count box above applies exactly that, so you can enter what one strand measures and read off what the bundle does.

The one thing it cannot capture is that a loosely-held bundle of strands spreads and covers differently from a single thread of the same total mass. The numbers match; the look does not quite.

Thread weight by fiber type: Different fibers at the same weight number may have different physical thicknesses because density varies. Polyester thread is slightly denser than rayon or cotton. Silk thread is finer at the same weight number compared to cotton.

Practical tips for choosing thread weight:

• 40-weight is the most versatile for machine embroidery and works with standard needles (75/11 or 80/12).
• Use a needle that matches the thread weight: heavier threads need larger needles, finer threads need smaller needles.
• Bobbin thread is typically 60-weight or lighter to reduce bulk on the back of the design.
• When mixing thread weights in a project, always test tension settings on scrap fabric first.
• Thread weight affects stitch density: lighter thread may need tighter stitch spacing to achieve full coverage.