Thread number: what it means, thickness table and decoding of systems

For many novice tailors and sewing masters thread number often becomes a source of confusion and errors when selecting consumables. The situation when, after sewing, puncture marks remain on the fabric or, conversely, the seam turns out to be too weak and cannot withstand the load, is usually caused by the wrong choice of thread thickness. Understanding how this parameter is labeled is a fundamental skill that separates the amateur from the professional in the world of sewing.

In this article, we'll take a closer look at why a lower number on a spool often means thicker thread, and how to avoid getting confused by the various marking systems. You'll learn about the metric system, the text system, and the denier system, and learn how to easily convert one value to another for the perfect result.

The main difficulty lies in the historical standards that are still used by different manufacturers around the world. If you are used to working with only one brand, changing suppliers can lead to unexpected results if you do not consider actual thickness fiber, and not just the number on the label.

Numbering principle: why less means thicker

The most common question that beginners have is: why is thread number 10 thicker than thread number 50? The answer lies in the so-called metric system numbering, which is most common in Europe and Russia. In this system, the thread number indicates the length of the thread in kilometers, which is contained in one kilogram of weight.

The logic here is simple and mathematically justified: if one kilogram of raw material contains 10 kilometers of thread, then it will be very thick and heavy. If 100 kilometers are drawn from the same kilogram of raw material, then the thread will turn out thin and light. That's why number 100 will be much thinner than number 30.

This system is convenient due to its linearity and predictability. Doubling the number means that the thread will become twice as thin (assuming the same twist density and material). However, in practice, manufacturers often add letter designations to the number or use mixed systems, which requires care.

• 🧵 The lower the number in the metric system, the thicker and stronger the thread is to break.
• 📏 Number 40-60 is considered universal for most household sewing tasks.
• ⚖️ The weight of the reel directly depends on the number: a reel with No. 10 will weigh more than a reel with No. 80 with the same winding length.

It is important to understand that the thickness of the thread affects not only the strength of the seam, but also its aesthetic appearance. Thread that is too thick on thin fabric will create a "accordion" or pinch effect and can also damage the structure of the material with the needle. On the other hand, a thin thread on thick jeans simply will not withstand the load and will burst the first time the product is used.

Text system and its features

Along with the metric system, the system is widely used in the clothing industry, especially when working with natural cotton and linen threads. texts (Tex or just Text). Here the principle is exactly the opposite of the metric one: the number indicates the weight in grams of a thread 1000 meters long.

In this system there is a direct relationship: the higher the number, the thicker the thread. For example, thread Text 30 will be three times thicker than the thread Text 10. This makes the text system more intuitive for those who are used to thinking that a larger number means a larger size or weight.

You can often find double markings on reels, for example, 40/2 or 20/3. The first number here indicates the number of component threads (warp), and the second number indicates the number of folds (twists). To get the final thread number in the metric system, you need to divide the first number by the second. So the thread 40/2 will have a final number of 20, and the thread 60/3 - number 20.

⚠️ Attention: When working with twisted threads (consisting of several layers), always pay attention to the number of twists. Threads 20/2 and 40/2 will have different thicknesses, despite the same second number, since they have different warps.

The text system is especially important when working with natural materials, since cotton and linen are often marked by weight of 1000 meters. This allows precise control of material consumption and fabric density, which is critical in industrial production.

Denier system for synthetics

The third most important system you will encounter, especially when working with synthetic materials (nylon, polyester, nylon), is the Denier (Den). It has historically developed for silk and synthetic fibers. The principle here is similar to the text system: the number indicates the weight in grams of a thread 9000 meters long.

In the Denier system, the rule also works: the larger the number, the thicker the thread. This system is indispensable when working with hosiery, light windbreakers, raincoat fabrics and parachute silk. You've probably seen the density designation for tights, for example, 20 Den or 40 Den - this is exactly the same system.

To convert Denier to texts, there is a simple formula: the Denier value must be divided by 9. For example, a 90 Denier thread will correspond to 10 Tex. Knowing this correspondence makes it easy to adapt to different types of raw materials if you don’t have the required coil at hand, but there is an analogue in a different measurement system.

Why 9000 meters?

Historically, a standard skein of raw silk weighed a certain amount, and a length of 9,000 meters was chosen as the base unit for calculating the weight of silk thread in some regions of Asia, where this standard originated.

Denier synthetic yarns often have high tensile strength with minimal thickness. This makes them ideal for products where lightness and moisture resistance are important, but shape retention is required. However, it is worth remembering that synthetics can melt under the influence of the high temperature of the iron or the friction of the needle.

Thread number correspondence table

So that you don’t have to make complex mathematical calculations or look for a conversion calculator every time, we have prepared a summary table of the correspondence of the main numbering systems. This will help you quickly navigate when purchasing consumables from different brands.

Metric number (Nm)	Lyrics (Tex)	Denier	Recommended Application
10	100	900	Line-by-line seams on leather, canvas, canvas
20	50	450	Denim, coat fabrics, upholstery
40	25	225	Dress fabrics of medium density, suiting
60	17	150	Thin blouse fabrics, silk, chiffon
80	12.5	112	The finest fabrics, embroidery, hemming work

Using this table, you can easily find an analogue if the store runs out of your usual threads. For example, if you need #40 thread and they don't have it, you can look for 25 Tex or 225 Den thread - it will be almost the same product.

How to choose thread numbers for different fabrics

Correct selection of thread numbers is the key to a high-quality and durable seam. Each type of fabric has its own optimal range of thread thickness, which provides a balance between the strength of the connection and the appearance of the product. Using the wrong thread can damage not only the seam, but also the fabric itself.

For light and delicate fabrics such as chiffon, organza, fine silk or cambric, it is necessary to use very fine threads, usually in the range №60-80 (metric number). Thicker thread here will look rough, may pull the fabric, causing wrinkles, or even cut through the fibers of the material when tensioned.

Medium-weight fabrics, which include most dress and suit materials, medium-weight cotton and linen, require threads №40-50. This is the most common range and is often called "universal". Such threads provide sufficient strength to the seam, while remaining thin enough to be invisible on the front side.

• 🧥 Thick coat fabrics, drape and gabardine are best sewn with threads No. 30-40.
• 👖 Threads No. 20-30 are ideal for denim, thick cotton and upholstery materials.
• 🎒 For leather, tarpaulin, canvas and technical fabrics, the thickest threads No. 10-20 are used.

Elastic and knitted fabrics deserve special attention. Here it is important not only the thickness, but also the stretchability of the thread. Often, a thinner thread is used for the bottom seam (shuttle) than for the top one to compensate for the tension. Also for knitwear, synthetic threads with the addition of elastane or special textured threads are often used.

⚠️ Attention: Never use thick threads (No. 10-20) for sewing light summer dresses or blouses. This will not only spoil the appearance of the product, but will also make the seam hard and brittle, which will lead to rapid wear of the item.

The influence of thread number on sewing machine settings

Changing the thread number is not just changing the spool in the bobbin case. Changing the thickness of the thread directly affects the settings of your sewing machine. If you switched from thread No. 40 to No. 60 or vice versa, you will definitely need to adjust the operating parameters of the mechanism.

First of all, it changes needle number. The thickness of the needle should correspond to the thickness of the thread so that the thread passes freely through the eye and does not get stuck or break. For threads No. 10-20, needles No. 100-120 are needed, for threads No. 40-50, needles No. 75-90, and for thin threads No. 60-80, needles No. 60-70.

Also subject to adjustment upper thread tension. A thinner thread requires less tension, otherwise it will pull the seam or break. Thick thread, on the other hand, requires a release of tension so that it can freely form a loop and be captured by the shuttle. Adjustment is made using the tension dial on the front of the machine.

Recommended needle settings:
Thread No. 10-20 -> Needle No. 100-120
Thread No. 30-40 -> Needle No. 90-100
Threads No. 50-60 -> Needle No. 75-90
Threads No. 70-80 -> Needle No. 60-70

Don't forget about the stitch length. For thick threads and fabrics, the stitch length is usually increased (3-4 mm) so that the seam does not look overloaded and the thread does not break due to frequent punctures. For thin fabrics and threads, the stitch length is reduced (2-2.5 mm) for greater strength and accuracy.

Common mistakes when choosing thread thickness

Even experienced craftsmen sometimes make mistakes when choosing the thread number, which leads to defective work. One of the most common mistakes is ignoring the type of fabric when choosing thread. Trying to sew thin synthetics with thick cotton thread is guaranteed to lead to tightening and deformation of the material.

Another mistake is using different thread numbers for the top and bobbin threads without setting the machine accordingly. Although this is sometimes acceptable (for example, when sewing thick fabrics when the bobbin thread is thinner), in standard situations it leads to poor quality stitching, looping or thread breakage.

Also, many neglect the quality of the thread itself, buying cheap options from unknown manufacturers, where the number may not correspond to reality. The spool may say No. 40, but in fact it will contain a thinner or, conversely, loose thread that will constantly break.

FAQ: Frequently asked questions

Can I use #10 thread on a regular sewing machine?

Using thread No. 10 in a regular household sewing machine is highly discouraged and even dangerous for the mechanism. Such thick threads are intended for industrial equipment or hand sewing. In a household machine, they can get stuck in the shuttle device, break the needle or damage the mechanism drive.

What to do if the thread number is erased from the spool?

If the marking is lost, you can determine the number visually and tactilely by comparing the unknown thread with reference samples. You can also weigh a piece of thread of a certain length (for example, 100 meters) and calculate the weight of 1000 meters (for the Tex system) or 1 km (for the metric system), although this is difficult to do at home without accurate scales.

What is the difference between 45LL and 65LL threads?

In the marking of Soviet and Russian threads, the letter “L” means lavsan (polyester), and “LL” means polished lavsan. The numbers 45 and 65 are the actual thread number in the metric system. 45LL thread is thicker and stronger than 65LL. They are universal synthetic threads, suitable for most fabrics.

How does thread number affect needle choice?

The thread number directly dictates the choice of needle number. The eye of the needle should be wide enough for the thread to pass through it freely, but not too large so as to disrupt the formation of the loop. The rule is simple: the thicker the thread (smaller number), the thicker the needle should be (larger needle number).