Crochet hook sizes in mm matter because US letter sizes and millimeter measurements do not always match cleanly across brands, which trips up anyone substituting a hook from a different manufacturer. A printed size chart taped inside your craft bin helps for exactly this reason. This guide gives the standard size conversion table.
The Size Chart
| US letter | Millimeters | Common use |
|---|---|---|
| B | 2.25mm | Thread and fine lace |
| E | 3.5mm | Sport weight yarn |
| H | 5.0mm | Worsted weight yarn, most common size |
| K | 6.5mm | Bulky weight yarn |
| P | 11.5mm | Super bulky and jumbo yarn |
The H hook at 5.0mm is the single most common size for worsted weight yarn, which is why most beginner patterns default to it.
Frequently asked questions
Do letter sizes match exactly across hook brands?
Mostly, but small variations exist between manufacturers. Always check the millimeter measurement on the hook itself rather than trusting the letter alone when substituting brands.
Need a garment size chart too?
Hook size is only one part of hitting your target finished measurements.
See the garment size chart
