Crochet Hook Size Converter

Convert crochet hook sizes between metric millimetres, US letter sizes and the old UK numbering.

A pattern that says "use a G hook" is unhelpful if your hooks are marked in millimetres, and old UK patterns number hooks backwards from the modern system. This converter reads across all three at once and shows the typical gauge each size produces.

At a glance

What you enter: Hook size (metric)
What you get: Size recognised, Suits bulky yarn and above, Suits fine yarn and below, Yarn weight class this suits
Formula shown: Yes, every step, right below your results.
Cost and privacy: Free, no account needed, and nothing you type is stored.

See worked examples ↓ Read the FAQ ↓ Share this calculator ↓

Hook size (metric)

Reset

Size recognised 1

Suits bulky yarn and above 0

Suits fine yarn and below 0

Yarn weight class this suits 1

How is this calculated?

Conversions come from the standard hook size chart, which fixes the metric size as the reference and maps the US letter and older UK number to it.

Where a size has no exact equivalent, the chart itself uses a range. The table below shows the chart in full so you can read across any size, not only the one you selected.

Gauge figures are typical values for single crochet in worsted weight. Your own gauge depends on your tension, the yarn and the stitch, so always swatch.

Crochet hook size chart

Metric	US	Old UK	Typical gauge (sc per 4 in)
2 mm	B/1	14	30
2.25 mm	B/1	13	28
2.5 mm	-	12	26
2.75 mm	C/2	11	25
3 mm	-	10	24
3.25 mm	D/3	9	23
3.5 mm	E/4	9	22
3.75 mm	F/5	8	21
4 mm	G/6	7	20
4.5 mm	7	6	19
5 mm	H/8	5	18
5.5 mm	I/9	4	17
6 mm	J/10	3	16
6.5 mm	K/10.5	2	14
7 mm	-	1	13
8 mm	L/11	0	12
9 mm	M/13	00	11
10 mm	N/15	000	10
12 mm	P/16	-	9
15 mm	Q	-	8
16 mm	-	-	7
19 mm	S	-	6
25 mm	-	-	5

Your numbers stay in the address bar, the link reproduces this exact calculation.

Results are estimates for general information only, always verify with a professional or official source before acting on them.

How to use the Crochet Hook Size Converter

1 Enter Hook size (metric)
2 Press Calculate. You get Size recognised, Suits bulky yarn and above, Suits fine yarn and below, Yarn weight class this suits, and every intermediate step stays visible under "How is this calculated?"
3 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.

Worked examples

Real numbers run through this calculator. Open any example to load it into the form above and change it.

US G hook

A US pattern calls for a G hook and yours are marked in millimetres.

You enter

Hook size (metric): 4

You get

Size recognised: 1
Suits bulky yarn and above: 0
Suits fine yarn and below: 0
Yarn weight class this suits: 1

G/6 is 4.00 mm.

Open this example in the calculator →

Bulky blanket

A chunky blanket pattern suggests a J hook.

You enter

Hook size (metric): 6

You get

Size recognised: 1
Suits bulky yarn and above: 1
Suits fine yarn and below: 0
Yarn weight class this suits: 2

J/10 is 6.00 mm, usually paired with bulky weight.

Open this example in the calculator →

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Frequently asked questions

What size is a G crochet hook?

A US G/6 hook is 4.00 mm. It is the workhorse size for worsted weight yarn and typically produces about 16 single crochet stitches per 4 inches, though your own tension decides the real number.

Why do old UK hook sizes run backwards?

The older UK system numbered hooks from large to small, so a higher number meant a finer hook, which is the opposite of the US letters and the metric sizes. That is why a vintage UK pattern can be genuinely confusing. Convert to millimetres first, then work from there.

Does the hook size on the yarn band matter?

It is a starting suggestion, not a rule. The band suggests a hook that produces a pleasing fabric with that yarn. If the pattern calls for a different gauge, change the hook until your swatch matches the pattern, not the band.

How much does one hook size change my gauge?

Roughly one stitch per 4 inches per 0.5 mm step in worsted weight, so two steps can move a 40 inch panel by well over an inch. That is why gauge matters more than the nominal size when fit is important.

Terms used here

Short, plain-language definitions of the words this calculator uses.

Yarn weight A category describing how thick a yarn is, published as a numbered system from 0 (lace) to 7 (jumbo) with an equivalent name such as fingering, DK, worsted or bulky.

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