Crochet thread sizes: chart from size 3 to size 100

Crochet thread sizes, from size 3 to size 100

Thread size	How thick	How common
3	the thickest size: about as thick as a thin yarn	one of the five common sizes
5	a little thinner than size 3	one of the five common sizes
10	thinner than most yarn: lace weight (0) in the standard yarn weight system	one of the five common sizes
20	finer than size 10	one of the five common sizes
30	finer than size 20	one of the five common sizes
40 to 100	the finest threads, in steps of 10; size 100 is the finest of all	less common than the five sizes above

A higher number is a finer thread: size 3 is the thickest on this chart and size 100 the finest.
Sizes 3, 5, 10, 20 and 30 are the common ones. Finer threads come in steps of 10, from size 40 to size 100.
Whatever the size, make a swatch and check it against the gauge your pattern states.

Thread numbers run the other way from yarn weight numbers. A yarn weight number rises as the yarn gets thicker. A thread size rises as the thread gets finer.
Crochet thread is usually cotton, often mercerized, and is used for fine work such as doilies and filet crochet.
Thread is worked with steel hooks, the small hooks that are numbered the other way round. The finer the thread, the smaller the hook.
Start from the hook your pattern names, then change it if your swatch does not match the gauge.

What is size 10 crochet thread equivalent to?: Lace weight, the thinnest category (0) of the standard yarn weight system. It is thinner than most yarn.
Which is thicker, size 10 or size 20 crochet thread?: Size 10. The higher the number, the finer the thread.
What hook do I use with size 10 crochet thread?: A steel hook of about 1.5 mm: a steel 7 or 8, depending on the maker. The standard gives steel hooks of 1.4 to 1.6 mm for thread of this weight.
What is the finest crochet thread?: Size 100.

What size hook do I need for size 20 or size 30 thread?: A smaller steel hook than for size 10: the finer the thread, the smaller the hook. Makers do not number steel hooks alike, so no number is given here. Start from the hook your pattern names and check your gauge.
Is crochet thread the same as yarn?: It is a kind of yarn: very thin, and sized on a scale of its own. Size 3, the thickest, is about as thick as a thin yarn. Size 10 and the sizes above it are finer than most yarn.

Abbreviations What does this abbreviation in my pattern mean?
US and UK terms What does this stitch name mean in US terms and in UK terms?
Chart symbols What does this symbol on a crochet chart mean?
Japanese chart symbols What does this symbol on a Japanese chart mean?
Terms in other languages What is this stitch called in a pattern written in another language?
Hook size for your yarn weight Which hook do I use with this yarn?
Hook size by project What size hook do I use for the thing I am making?
Hook size chart What size is my hook, in millimeters and as a US letter or number?
Steel hook sizes What size is my steel crochet hook in millimeters?
Knitting needle to hook size Which crochet hook is the same size as my knitting needle?
Yarn weight chart What weight is my yarn, and what else is it called?
Starting chain calculator How many chains do I start with for this width?
Yarn calculator How much yarn do I need to finish this?
Blanket size chart How big should I make this blanket?
Baby blanket size chart How big should I make a baby blanket?
Scarf size chart How long and how wide do I make a scarf?
Hat size chart How big is the head I am making this hat for?
Size chart for babies How big are a baby's head and feet at this age?
Headband size chart How long do I make a headband or an ear warmer?
Slipper size chart How long is the foot for this shoe size?
All crochet tools