Convert crochet hook sizes between millimetres, US letter sizes and old UK sizes, and see the full chart at a glance.
Convert a hook size
Choose the system you know, pick the size, and see the other two.
Hook sizing is not perfectly standardised. Brands differ a little, so check the size marked on your hook.
How it works
Three steps, a few seconds.
Pick a system
Choose mm, US or UK, then pick the hook size you have.
Press Convert
The other two sizes appear, and the matching row is highlighted in the chart.
Check the chart
Use the full table to compare sizes side by side.
Why hook sizes are confusing
Crochet hooks are labelled in three different ways. Millimetres measure the width of the hook shaft and are the most reliable. US sizes use letters and numbers, such as G-6 or H-8. Older UK sizes use numbers that count down as the hook gets bigger, from 14 for fine hooks to 000 for very large ones. Some sizes exist in one system but not the others, which is why some rows below show a dash.
Which size should I use?
Use the hook size in your pattern as a starting point, then make a gauge swatch. If your swatch is too small, switch to a larger hook. If it is too large, use a smaller one. The millimetre size is the safest number to compare, because letters and numbers vary between brands.
Frequently asked questions
What size is a G-6 hook?
A US G-6 hook is 4.0 mm. In old UK sizing it is a size 8.
Is a bigger number a bigger hook?
In millimetres and US sizes, yes. In old UK sizes it is the opposite: the number goes down as the hook gets bigger.
Are all brands exactly the same?
No. Hooks that share a size label can differ slightly between brands, so measure the shaft if you need to be sure.
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