Free knitting & crochet tools

Crochet Hook Size Converter

A pattern says H, your hooks say millimetres, and the vintage booklet says 6. Type any of them and get the other two, plus the full US, metric and UK chart.

Crochet hook size chart

A dash means that system has no size at that millimetre. Steel hooks for thread crochet use a separate, reversed US scale (a US 14 steel hook is 0.75 mm) and aren't in this chart.

How the three systems work

Metric is the diameter of the hook shaft in millimetres, and it's the only one of the three that is a measurement rather than a name. Two hooks marked 5 mm are the same size whoever made them. When you buy hooks or write down what a project used, use millimetres.

US sizes are letters, with a number alongside on most modern hooks: G-6 is 4 mm, H-8 is 5 mm, I-9 is 5.5 mm, and so on. The letters go up with the size, but not evenly, and the numbers skip. Some manufacturers also disagree at the edges: an "N" hook is 9 mm from one maker and 10 mm from another, which is why the chart shows M/N and N/P where the letters overlap. If a pattern gives only a letter and the result matters, check its metric size.

UK and Canadian sizes are the old imperial wire gauge, and they run backwards: a bigger number is a smaller hook. UK 6 is 5 mm, UK 3 is 6.5 mm. You'll meet them in vintage patterns and in some current British ones. Modern UK patterns almost always give millimetres as well.

Which hook for which yarn

The yarn label's recommended hook is the starting point, not the rule. The table below is what the Craft Yarn Council suggests per weight; your gauge swatch decides. If your stitches come out tighter than the pattern's gauge, go up a half millimetre; looser, go down. The yarn weight converter identifies an unlabelled yarn, and the gauge calculator turns a swatch into stitch counts.