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πŸͺ‘ Crochet Hook Size Converter (US / UK / mm)

Convert between US, UK, and metric (mm) crochet hook sizes in one place.

mm (Metric)
β€”
US Size β€” mm (Metric) β€” UK Size β€”
Crochet Hook Size Conversion Table
USmmUK
B-12.2513
C-22.7512
D-33.2510
E-43.59
F-53.758
G-64.07
74.56/7
H-85.06
I-95.55
J-106.04
K-10.56.53
L-118.00
M/N-139.000
N/P-1510.0000
P/Q15.0β€”
Q16.0β€”
S19.0β€”
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GUIDE

Learn more

01

Understanding Crochet Hook Size Systems

Crochet hook sizes are labeled differently depending on country and brand. US sizes use a letter/number combination (B-1, C-2, …). UK sizes run in the opposite direction β€” a larger number means a thinner hook. mm (metric) is the international standard indicating the hook's actual diameter. Following overseas (especially UK/European) patterns can be confusing due to these differences, which is when conversion becomes necessary.

The most reliable reference is always the mm diameter, since actual diameter can vary slightly by brand even at the "same" labeled size β€” for projects where gauge precision matters, measure with calipers or a hook gauge.
02

Crochet Hook Size Conversion Table

Below is the standard conversion table between US, metric (mm), and UK crochet hook sizes. A dash ("β€”") means there is no standard equivalent in that system.

USmmUK
B-12.2513
C-22.7512
D-33.2510
E-43.59
F-53.758
G-64.07
74.56/7
H-85.06
I-95.55
J-106.04
K-10.56.53
L-118.00
M/N-139.000
N/P-1510.0000
P/Q15.0β€”
Q16.0β€”
S19.0β€”

This table follows the standard crochet hook size conversion commonly published by the Craft Yarn Council and major yarn manufacturers.

Frequently asked questions

Why do US crochet hook sizes combine a letter and a number?
US crochet hook sizing historically started with letters (B, C, D…) and later added a numeric scale, leading to the common "B-1", "C-2" combined labeling. The mm (metric) size is always the most accurate reference.
What do I do about sizes marked "β€”" in the table?
That means there is no standard equivalent defined in that sizing system. In that case, use the mm (metric) diameter as your reference, or buy a hook labeled in mm for the most accurate match.
Do hooks of the same US size vary in actual diameter by brand?
Slightly, yes. For projects where gauge precision matters, measure your hook's actual diameter with calipers or a hook gauge rather than relying on the labeled size alone.