Yarn vs Thread: What's the Difference and When to Use Each

Quick answer: In the yarn vs thread question, the short version is thickness and purpose. Yarn is the thicker strand you knit, crochet or weave with, sized on the Craft Yarn Council’s 0 to 7 scale. Thread is a fine, tightly twisted strand built for sewing, sized by weight (40 wt, 50 wt) or Tex. Use yarn to make fabric. Use thread to join it.

There’s one honest wrinkle. Technically, thread is made from yarn.

Coats, a major industrial thread maker, describes thread as more than one ply of yarn twisted together. So the line between them is about how the strand is finished and what it’s built to do, not some completely separate material.

In everyday craft terms, though, the split is clear. I’d sort it like this: if it goes on a hook or knitting needles, it’s yarn. If it goes through the eye of a sewing needle or a sewing machine, it’s thread.

Simple rule. In my reading of the makers’ own charts, it holds up surprisingly well.

Yarn vs Thread at a Glance

	Yarn	Thread
Main use	Knitting, crochet, weaving	Sewing by hand or machine, quilting, embroidery
Thickness	Thicker, from lace to jumbo	Fine
How it’s sized	Craft Yarn Council weights 0 to 7	Weight (wt), Tex or ticket number
Size direction	Higher number = thicker	Weight: higher number = finer. Tex: higher = heavier
Tools	Knitting needles, crochet hooks, looms	Sewing needles, sewing machines
Gauge or fit measured by	Stitches per 4 inches	Thread weight matched to needle size
Crossover product	Lace weight (category 0)	Crochet thread, worked with steel hooks

How Yarn Is Sized

The Craft Yarn Council’s Standard Yarn Weight System runs from 0 to 7, thinnest to thickest:

• 0 Lace: fingering and 10-count crochet thread
• 1 Super Fine: sock, fingering, baby
• 2 Fine: sport, baby
• 3 Light: DK, light worsted
• 4 Medium: worsted, afghan, aran
• 5 Bulky: chunky, craft, rug
• 6 Super Bulky: super bulky, roving
• 7 Jumbo: jumbo, roving

Each category comes with suggested needle and hook sizes and a typical gauge, counted in stitches per 4 inches. For a medium (4) yarn, the council lists knitting needles of 4.5 to 5.5 mm and crochet hooks of 5.5 to 6.5 mm.

The council calls these guidelines only. Its advice is to always follow the gauge stated in your pattern, and I’d treat that as the rule that beats every chart. If you’re matching a hook to a yarn, our guide on what size yarn for a 5mm crochet hook walks through it with the chart.

How Thread Is Sized

Thread uses completely different systems, and they don’t even agree on which direction is bigger. When you shop for thread, I’d check which system the label uses before comparing two spools.

The Weight System

This is the label most home sewists see: 40 wt, 50 wt, 80 wt. Aurifil explains that under this system, the higher the number, the finer the thread.

It’s based on a measure called Number English (Ne), the number of 840-yard hanks of material that weigh 1 pound. A 50 wt thread means 50 hanks, about 42,000 yards, weigh a pound.

Tex

Coats describes Tex as a fixed-length system: the weight in grams of 1,000 metres of thread. So Tex 40 means 1,000 metres weighs 40 grams.

Here a higher number means a heavier, coarser thread. The opposite direction from weight.

Ticket Numbers

Coats calls ticket numbers a commercial system, essentially a manufacturer’s reference for size. It warns that a ticket number in one type of thread won’t match the same number in another type.

Higher ticket numbers mean finer thread. For synthetic threads, Coats gives a conversion: divide 1,000 by the Tex number, then multiply by 3.

Why the Systems Run in Opposite Directions

This confused me until I looked at what each one actually measures. Weight counts how much length it takes to reach a fixed weight, so a finer thread needs more hanks to make a pound and gets a bigger number. Tex does the reverse: it fixes the length at 1,000 metres and weighs it, so a thicker thread weighs more and gets a bigger number.

Same thread, two opposite labels. Once you see that, the numbers stop feeling random.

My take: when comparing two spools from different brands, ignore the ticket and look for the weight or Tex. Those two are at least defined. And don’t read anything into yarn “weight” either, because a category 4 yarn label describes thickness, not how heavy the ball is.

What Each Thread Weight Is For

Aurifil, a thread maker, gives practical uses for its common weights:

• 12 wt: big stitch hand quilting
• 28 wt: bold machine stitching, or texture by hand
• 40 wt: greater stitch definition in quilting
• 50 wt: thinner than 40 wt and ideal for piecing
• 80 wt: superfine detail

Aurifil also matches needles to weights. For 50 wt and 40 wt, it suggests an 80/12 microtex, universal or denim needle.

For 12 wt it suggests a 100/16 or 90/14 topstitch needle, and for 28 wt a 90/14 topstitch, quilting or denim needle. At the fine end, 80 wt pairs with a 70/10 or 80/12 microtex or embroidery needle. The pattern is easy to remember: heavier thread, bigger needle.

Can You Use Yarn in a Sewing Machine?

Not as the main thread. Yarn is far too thick to pass through a sewing machine needle’s eye, which is sized for thread weights like the ones above. Even Aurifil’s heaviest 12 wt thread already calls for a large 100/16 or 90/14 topstitch needle.

Don’t try to force it. If you want the look of yarn on fabric, my suggestion is to lay it on top and stitch over it with ordinary thread, so the thread still does the sewing.

Can You Crochet With Thread?

Yes, with the right kind. Crochet thread is its own product, and the Craft Yarn Council puts 10-count crochet thread in its category 0 (Lace). It’s worked with steel crochet hooks, which the council lists at 1.4 to 1.6 mm, or a regular 2.25 mm hook.

Here’s the part most people miss, in my view. The council says steel hooks are sized the reverse of regular hooks: the higher the number, the smaller the hook. So a steel size 8 is smaller than a steel size 6.

Ordinary sewing thread is a different story. It doesn’t appear on the council’s yarn chart at all, because it’s sized for sewing needles, so I’d stick with proper crochet thread for crochet.

Which Should You Choose?

• Choose yarn if you’re knitting, crocheting, weaving or making anything where the strand itself forms the fabric. Pick the weight your pattern names, then check gauge.
• Choose sewing thread if you’re joining fabric by hand or machine. A 50 wt thread suits everyday piecing and seams, according to Aurifil.
• Choose a heavier thread (12 wt to 28 wt) for visible decorative stitching or hand quilting, with a needle sized to match.
• Choose crochet thread for doilies, fine lace and edgings, with steel hooks.

If you sew and embroider as well as knit, our embroidery machine vs sewing machine guide covers the machine side. More yarn guides are in Yarn Crafts.

Frequently Asked Questions

Is Thread Just Thin Yarn?

In a technical sense, partly. Coats describes thread as plies of yarn twisted together. In crafting, thread means a fine strand made for sewing, while yarn means the thicker strand used to knit and crochet.

Is Crochet Thread the Same as Yarn?

Crochet thread is a very fine yarn. The Craft Yarn Council puts 10-count crochet thread in category 0 (Lace), and it’s worked with small steel hooks.

Does a Higher Thread Weight Mean Thicker Thread?

No. In the weight system, a higher number means finer thread, so 50 wt is thinner than 40 wt. In the Tex system, a higher number means heavier thread.

Which Thread Weight Is Best for Everyday Machine Sewing?

Aurifil describes its 50 wt as thinner than 40 wt and ideal for piecing, and pairs it with an 80/12 needle. That makes 50 wt a sensible starting point for general seams.

Last updated: November 10, 2026. Sources: Craft Yarn Council: Standard Yarn Weight System, Coats: thread numbering and Aurifil: thread FAQ.