Thread weight is one of those numbers that's easy to ignore until a project doesn't look right. The seam is bulky, or the quilting disappears into the fabric, or the embroidery fills in too heavily — and the thread is usually why.
In this tutorial, Heidi from ThreadWorks explains what thread weight numbers actually mean and covers the full range you'll come across in sewing, quilting and embroidery: from 12wt all the way to 80wt, and when it makes sense to reach for something other than standard 50wt.
What you'll learn
- What the number on a spool of thread is actually measuring
- Why 50wt is the default for so much sewing and piecing
- Where heavier threads down to 12wt earn their place
- Where fine threads up to 80wt are the better choice
The number runs backwards
This trips up almost everyone at first: with thread weight, a higher number means a finer thread. 80wt is very fine. 12wt is thick and highly visible. 50wt sits in the middle and is the reason it's the everyday default — it's strong enough for construction seams but fine enough that it doesn't add bulk where seams meet.
Matching thread to the job
Piecing is where fine thread pays off. Every seam allowance in a quilt block holds thread, and a bulky thread multiplied across dozens of intersections is what makes blocks refuse to lie flat.
Decorative work is the opposite. If you want the stitching to be seen — topstitching, big-stitch quilting, visible hand-look detail — a heavier thread is doing the job you're asking of it. And your needle has to keep up: heavier thread needs a larger eye, which is a needle change, not a tension adjustment.
Where to go next
Our Quilting Thread Weights Explained guide goes deeper on 40wt vs 50wt specifically, and How to Choose the Right Sewing Thread covers fibre and finish as well as weight.
Because thread weight and needle size go together, Sewing Machine Needle Sizes & Types Explained is worth reading alongside it.
Shop sewing thread, quilting thread, embroidery thread and machine needles.