Conversion chart
Crochet hook sizes, without the guesswork.
Match by metric diameter first. US letters and numbers are convenient labels, but they can vary between manufacturers—and steel hooks use a separate reverse numbering system.
Metric diameter is the reliable comparison. Letter and number labels can vary by manufacturer.
Source-backed reference
Metric to US crochet hook chart
The table uses Craft Yarn Council pairings. Blank or multi-letter entries are kept explicit instead of forcing a false one-to-one conversion.
| Metric | US label | Guide |
|---|---|---|
| 2 mm | Steel 4 (not a regular-hook letter size) | Open |
| 2.5 mm | No single CYC US label | Open |
| 3 mm | No single CYC US label | Open |
| 3.5 mm | E-4 | Open |
| 3.75 mm | F-5 | Open |
| 4 mm | G-6 | Open |
| 4.5 mm | 7 | Open |
| 5 mm | H-8 | Open |
| 5.5 mm | I-9 | Open |
| 6 mm | J-10 | Open |
| 6.5 mm | K-10½ | Open |
| 7 mm | No single CYC US label | Open |
| 8 mm | L-11 | Open |
| 9 mm | M/N-13 | Open |
| 10 mm | N/P-15 | Open |
Two systems
Regular and steel hooks are not numbered alike.
Regular hooks: metric diameter generally increases with the common letter or number size.
Steel hooks: a higher US number means a smaller hook. The Craft Yarn Council also notes variation within steel numbering.
See a steel-size exampleStep 1Find the metric diameter printed on the hook or package.
Step 2Use the chart to find the common US label—without assuming it is universal.
Step 3Swatch in the pattern stitch and adjust until your measured gauge matches.
Source notes
Last reviewed September 1, 2026
- Craft Yarn Council: Hooks & Needles Metric and US hook and needle size tables; gauge-swatch qualification.
- Craft Yarn Council: Steel Crochet Hook & Crochet Thread Sizes Steel-hook numbering and its reverse relationship to hook diameter.
- Craft Yarn Council: Standard Yarn Weight System Yarn weight categories, common names, gauge ranges, and tool ranges.