40 Wt Thread: What It Is Used For, Needle Size and Brands
40 wt thread is medium. It is used for machine quilting with stitch definition, machine embroidery (standard weight), topstitching, piecing, with a 80/12 Microtex, Sharp, Universal, or Denim (Aurifil 40 wt); 90/14 Topstitch (Superior King Tut and Fantastico) needle as a starting point. In the weight system, a higher number means finer thread: 40 wt means 40 kilometers of thread weigh 1 kilogram. Common examples include Aurifil 40 wt and Superior King Tut 40 wt.
Thread weight (wt) is an inverse measure: the higher the number, the finer the thread. In the common weight system, the number is the kilometers of thread that weigh 1 kilogram. 40 wt means 40 km weighs 1 kg (Superior Threads).
| Thickness | Medium |
|---|---|
| Common uses | Machine quilting with stitch definition, Machine embroidery (standard weight), Topstitching, Piecing |
| Machine needle | 80/12 Microtex, Sharp, Universal, or Denim (Aurifil 40 wt); 90/14 Topstitch (Superior King Tut and Fantastico) |
| Example threads | Aurifil 40 wt, Superior King Tut 40 wt, Superior Fantastico 40 wt, Isacord 40 (polyester embroidery) |
| Next heavier | 30 wt |
| Next finer | 50 wt |
| Notes | The most common machine embroidery thread weight. |
How does 40 wt compare with other thread weights?
| Weight | Thickness | Typical uses | Needle |
|---|---|---|---|
| 12 wt | Very heavy | Big-stitch hand quilting, Bold machine quilting, Decorative topstitching | 90/14 or 100/16 Topstitch (Aurifil 12 wt) |
| 28 wt | Heavy | Machine quilting with visible texture, Hand quilting, Blanket stitch applique | 90/14 Topstitch, Quilting, or Denim (Aurifil 28 wt) |
| 30 wt | Medium heavy | Decorative stitching, Quilting that should show, Some embroidery | 90/14 is a common starting point |
| 40 wt | Medium | Machine quilting with stitch definition, Machine embroidery (standard weight), Topstitching | 80/12 Microtex, Sharp, Universal, or Denim (Aurifil 40 wt); 90/14 Topstitch (Superior King Tut and Fantastico) |
| 50 wt | Fine | Piecing with flat seams, Garment sewing, Machine applique | 80/12 Microtex, Sharp, Universal, or Denim (Aurifil 50 wt); 90/14 Topstitch (Superior So Fine! 50) |
| 60 wt | Fine | Bobbin thread for embroidery and quilting, Fine piecing, Heirloom sewing | 90/14 Topstitch (Superior Bottom Line); 70/10 to 80/12 also used |
| 80 wt | Very fine | Invisible machine and hand applique, Heirloom sewing, Fine detail quilting | 70/10 or 80/12 Microtex, Sharp, or Embroidery (Aurifil 80 wt) |
| 100 wt | Ultra fine | Micro-stippling and dense background quilting, Invisible applique, Heirloom machine quilting | 70/10 Topstitch (Superior MicroQuilter); 70/10 or 80/12 Microtex on domestic machines |
Which needle size goes with each thread weight?
Match the needle to both the fabric and the thread. This Schmetz-based chart shows the thread weights usually paired with each needle size.
| Needle size | Thread weights | Typical fabrics |
|---|---|---|
| 60/8 | 80 to 100 wt | Silk chiffon, Organza, Batiste |
| 65/9 | 60 to 100 wt | Silk, Fine and highly elastic knits, Lingerie fabrics |
| 70/10 | 60 to 80 wt | Lawn, Voile, Silk |
| 75/11 | 50 to 60 wt; 40 wt embroidery thread on an Embroidery 75/11 | Lightweight to medium knits, Quilting cotton piecing, Machine embroidery |
| 80/12 | 40 to 50 wt | Quilting cotton, Shirting, Poplin |
| 90/14 | 28 to 40 wt; heavier threads on a Topstitch needle | Light to medium denim, Twill, Corduroy |
| 100/16 | 12 to 30 wt (use a Topstitch needle for 12 wt) | Heavy denim, Canvas, Upholstery |
| 110/18 | Heavy and topstitching threads | Heavy canvas, Upholstery, Heavy denim |
| 120/19 | Heavy thread | Very heavy canvas, Upholstery, Vinyl |
Test on a scrap first
Sew a few inches through the same layers as your project. If the top thread loops underneath or shreds, change the needle before touching tension.
Thread and machines for 40 wt work
Simthread 120 Color Polyester Embroidery Thread Kit
$71.99A 120 color set of 40 wt polyester embroidery thread for home embroidery machines.
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Isacord Embroidery Thread Set, 35 Cones
$189.99Isacord 40 wt cones, a professional standard for multi-needle and business embroidery.
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Madeira Polyneon 40 Clear Box Astro 18-Spool Thread Set
$69.41A clear box of Madeira Polyneon 40 wt in 18 colors.
Check pricePrices change often, so confirm on Amazon. As an Amazon Associate we earn from qualifying purchases.
Frequently asked questions
What is 40 wt thread used for?
40 wt thread is used for machine quilting with stitch definition, machine embroidery (standard weight), topstitching, piecing. It is described as medium. It sits in the middle of the range, strong enough for everyday seams and fine enough to stay out of the way. The most common machine embroidery thread weight.
What needle should I use with 40 wt thread?
Start with a 80/12 Microtex, Sharp, Universal, or Denim (Aurifil 40 wt); 90/14 Topstitch (Superior King Tut and Fantastico) needle for 40 wt thread. The needle eye must be large enough for the thread to pass without shredding, so heavier threads need bigger needles and topstitch needles with longer eyes. If the thread frays or breaks, move up one needle size before adjusting tension.
Is 40 wt thread thicker than 50 wt?
Yes. Thread weight is an inverse measure, so the lower number is the thicker thread. 40 wt is heavier than 50 wt, which is fine. Thread weight (wt) is an inverse measure: the higher the number, the finer the thread.
Can I use 40 wt thread in the bobbin?
Yes, 40 wt works in the bobbin on most machines. Many quilters match the bobbin weight to the top thread for balanced tension, while others choose a finer bobbin thread so more fits on the bobbin. Test on a scrap sandwich and adjust tension until neither thread shows on the wrong side.
What brands make 40 wt thread?
Examples of 40 wt thread include Aurifil 40 wt, Superior King Tut 40 wt, Superior Fantastico 40 wt, Isacord 40 (polyester embroidery). Brands label weight differently: some use the weight system and others use cotton count, such as 50/2 on Aurifil spools. Aurifil labels cotton with the Ne (Number English) cotton count: the number of 840 yd hanks that weigh 1 lb.
How we research: we compare manufacturer specifications, owner manuals, published standards and recurring themes in verified owner reviews. We do not test products in person, and this is researched guidance, not professional advice. Follow your machine manual and pattern, and take care with rotary cutters, hot irons and needles. As an Amazon Associate we earn from qualifying purchases.