How to choose sewing thread is a question many people underestimate – yet the thread decides whether a seam holds, puckers or shows. The wrong weight can tear a fine fabric or keep snapping when you sew denim. In this guide we explain what the numbers on the spool mean, how to pair thread with the right needle and how to choose a colour.
What the thread number means
Sewing threads are most often labelled with the metric count (Nm), which tells you how many metres of thread are made from one gram of material. So the rule is: the higher the number, the finer the thread.
- No. 120 thread – finer, giving a neat, almost invisible seam.
- No. 80 thread – heavier and stronger, suited to stressed seams and decorative topstitching.
You may also see Tex ratings, which work the other way round: a higher number means a thicker thread. Roughly, No. 120 corresponds to about Tex 25 and No. 80 to about Tex 35–40.
Which number for which fabric
| Fabric / garment | Recommended thread | Needle (Nm) |
|---|---|---|
| Shirts, blouses, poplin, viscose, lingerie | No. 120 | 70–80 |
| Dresses, light trousers, jersey | No. 120 | 75–90 (stretch needle for knits) |
| Suiting, skirts, jackets | No. 120 or No. 80 | 80–90 |
| Denim, workwear, canvas | No. 80 | 90–110 |
| Decorative topstitching, bags | No. 80 | 100–110 |
Thread and needle must match. If the thread is too thick for the needle, it rubs in the eye, frays and breaks. If the needle is too heavy for the thread, it leaves visible holes in fine fabrics.
How to choose the colour
- Matching – lay the spool on the fabric in daylight. If there is no exact match, go one shade darker; it disappears better than a lighter one.
- Prints – match the thread to the dominant colour of the pattern.
- Contrast stitching – red or white thread on a dark fabric is used deliberately as a design feature.
- Denim – classic jeans topstitching uses indigo or a contrasting copper/yellow thread; for hemming jeans, indigo is the least noticeable choice.
Black and white threads are the foundation of every sewing box and cover most repairs and everyday projects.
A basic thread kit for home sewing
If you are just putting together a sewing box, you do not need dozens of spools. Start with black and white in No. 120 for shirts, blouses and light fabrics, plus the same colours in No. 80 for trousers, jackets and heavier cloth. Add indigo for denim and one bright colour, such as red, for marking and decorative seams. With these six spools you can handle almost any repair, from sewing on a button to shortening jeans.
Tips for better seams
- Use the same thread in the needle and the bobbin unless you want a contrast underneath.
- Test the tension on a scrap of the same fabric before sewing the garment.
- Keep spools away from direct sunlight and dust – old, dried-out thread loses strength.
- When hand-sewing buttons, use the thread doubled so that No. 120 is strong enough.
Frequently asked questions
Which thread is thicker – 80 or 120?
No. 80 is the thicker thread. With metric numbering, a lower number means a heavier thread.
Can I sew jeans with No. 120 thread?
For repairs and inside seams, yes. For visible topstitching and jeans hems, No. 80 gives a stronger and more authentic result.
Why does my thread keep breaking?
The most common causes are a needle that is too fine or blunt, tension set too tight, or thread that is too heavy for the needle. Change the needle and loosen the tension.
Pick the right weight and colour from our sewing threads, and finish the garment with something from our buttons range.
