What do crochet hook sizes mean?
A crochet hook consists of a long handle with a hook at one end. As you work through your project, you'll slip yarn over that hook to create stitches. Crochet hooks come in all different sizes. If you're working with thin yarn to create delicate lace, you'll want a smaller one; on the other hand, a blanket made from chunky yarn will require a much larger hook.
How are crochet hooks measured? Just to confuse things, there are several different size systems. Some use letters, others numbers, others metric measurements. However, one thing that all crochet hook sizes have in common is that they measure the diameter of the hook's shaft.
A crochet hook conversion chart, as shown below, can help explain the differences between systems. In general, the USA uses letters, which go up as the hook gets bigger (so a C hook is bigger than a B, for example). Japan uses ascending numbers, with a 2 hook being very small and a 10 being very large. Confusingly, the UK used to use descending numbers: a 14 is tiny, while a 1 is extremely large. Nowadays, though, most crochet hooks in the UK are sold with metric measurements, with the diameter of the shaft indicated in millimetres.
How to measure a crochet hook
Many crochet hooks will have the size printed or embedded somewhere on the handle. However, that isn't always the case. Trying to measure a crochet hook by sight is extremely tricky, as the difference between two sizes can be very small. It's best to use a crochet hook gauge to check sizes. These handy tools have holes in them. Slip your hook through the holes to test its size. Your hook should fit very snugly into the hole of the right size.
Crochet hook size chart
If you're buying crochet hooks nowadays in the UK, you can expect them to be sold with metric measurements. However, older crochet hooks or hooks that you bought abroad might use a different system. If you're using an older British pattern, or patterns from the US or Japan, it's important to know how to convert sizes. This chart will help you.