2026-08-14 · Tools, Hooks & Yarn · Beginner/Intermediate
Crochet Hook Sizes Explained: Metric, US, and UK Conversion Chart
Confused by hook sizing letters and numbers? Here's a clear breakdown of metric, US, and UK crochet hook sizes so you can pick the right tool every time.
Why Hook Sizes Can Be Confusing
If you've ever picked up a hook labeled H-8 and another labeled 5mm and wondered if they're the same thing, you're not alone. Crochet hooks are sized using three different systems: metric (millimeters), US letters and numbers, and UK numbers. To make things trickier, US and UK sizing don't always line up neatly, and older UK hooks can differ slightly from newer standards.
The good news is that metric sizing is the most reliable, since it measures the actual diameter of the hook shaft. Whenever a pattern gives you a millimeter size, use that as your anchor.
Here's a quick conversion chart for common sizes:
| Metric (mm) | US | UK | |---|---|---| | 2.25 | B-1 | 13 | | 3.5 | E-4 | 9 | | 4.0 | G-6 | 8 | | 5.0 | H-8 | 6 | | 6.0 | J-10 | 4 | | 8.0 | L-11 | 0 |
Keep this chart handy, especially if you're following patterns from different countries. When in doubt, measure your hook with a gauge tool or ruler rather than trusting the printed label, since manufacturers sometimes vary slightly.
Understanding these conversions will save you from frustration and help your stitches turn out the size the pattern intended.