Crochet Hook Size Chart

Why sizing isn't consistent

US letter sizes and old UK/Canada sizes were standardized decades apart by different organizations, and neither system was built with the other in mind — that's why they don't convert on a clean 1:1 basis. Two hooks with different letters can be the exact same metric size, and a single letter (like G) can map to a different millimeter size depending on which country's chart you're reading. When following a pattern from a different region, match the metric millimeter size if it's given at all, since that's the one measurement that's physically the same regardless of what a manufacturer printed on the handle.

When the size stamped on the hook is worn off

Cheap or older hooks sometimes lose their printed size entirely. Rather than guessing, lay the hook's shaft across a ruler or gauge tool with pre-cut holes sized to standard hook diameters — the size that fits snugly (not loosely, not forced) is the real one. Steel hooks used for thread crochet run on a completely separate numbering scale from the lettered aluminum/plastic hooks used for yarn, and confusingly the numbers run in the opposite direction: a steel size 12 is much finer than a steel size 1, while a lettered B-1 is smaller than a K-10.5. If a thread pattern calls for a steel hook, don't substitute a same-numbered yarn hook — they aren't related sizes at all.