Crochet Hook Size Converter

How to Convert Crochet Hook Sizes

Crochet hooks are sized by the diameter of the shaft in millimetres, but each region labels that diameter differently. The US uses a letter and number combination (like H/8), the UK and Canada use a single number that runs in the opposite direction, and metric measurements are the universal standard. Our Crochet Hook Size Converter instantly translates between all three systems so you can confidently follow any pattern from any country.

Understanding the Three Hook Size Systems

The metric system is the most precise and least ambiguous. A 5.0mm hook measures exactly 5 millimetres across the shaft. The US system pairs a letter with a number where larger letters mean larger hooks. The UK and Canada system uses a single number that decreases as the hook gets larger, so a UK 14 is only 2mm while a UK 2 is 7mm. Because these systems run in opposite directions, always convert through the millimetre size for accuracy.

Steel Hooks for Thread Crochet

Steel hooks used for fine thread crochet, doilies, and lace work have their own separate numbering scale. A US steel 1 is 2.75mm while a US yarn B/1 is 2.25mm, so the same number can mean a completely different size depending on whether it is a yarn hook or a steel hook. Our converter includes a dedicated steel hook mode with its own conversion table so you never confuse the two.

Why Gauge Still Matters

Even with the correct hook diameter, your personal tension affects the finished size of your project. Always crochet a gauge swatch and compare it to the pattern recommendations. If your swatch is too tight, go up one hook size. If it is too loose, go down one size.

For other measurement conversions, try the Shoe Size Converter, Knitting Needle Size Converter, and Unit Converter.