Crochet Hook Size Chart

Crochet hook sizes are labeled differently depending on where you are: US patterns use a letter-number system (B-1, G-6, J-10), while the rest of the world uses metric millimeters. Metric mm is the universal constant — a 6.0 mm hook is 6.0 mm on any continent.

How it works

The table maps US letter/number labels, metric diameters, and old UK/Canadian numbers across all standard sizes. The shaft diameter in mm is the most reliable reference because:

• Some US letters are used inconsistently between manufacturers (e.g. G can be 4.0 or 4.25 mm depending on brand)
• UK/Canadian numbers run in the opposite direction to US numbers

Practical examples

Example 1 — Pattern says H-8. Look up H-8 in the table: H-8 = 5.0 mm. Check your hook's shaft for the engraved mm size before starting.

Example 2 — UK pattern calls for size 8. Old UK size 8 = 4.0 mm = US G-6. Note: old UK numbers decrease as hook size increases.

Example 3 — Your tension is too tight. Your gauge swatch is tighter than the pattern specifies. Move up one hook size — if using 5.0 mm (H-8), try 5.5 mm (I-9).

Common mistakes

• Trusting the US letter alone. Some manufacturers label 4.0 mm as G-6 and others as G-7. Always confirm the mm size engraved on the hook.
• Confusing standard and steel hooks. Steel hooks for thread crochet use a separate, reversed numbering system (higher number = smaller hook). This table covers standard aluminum/wood hooks only.
• Skipping the gauge swatch. Hook size + yarn + your tension all combine to determine gauge. Always swatch before a sized project.

International and regional variations

Quick reference

For a side-by-side view of all crochet hook sizes, knitting needle sizes, and yarn weight recommendations in one page, see the Knitting Needle & Crochet Hook Size Chart →.