Have you ever come across a pattern that called for a “G” hook (or maybe some other letter)? Possibly you wondered what size hook that was? Here in the US, hooks are given a letter and/or a number to assign what size they are. A lot of countries go with the metric hook sizes. I personally prefer to go with the metric sizing, because it denotes an actual measurement of the hook. It allows less margin of error since a 4 mm hook will in fact be 4 mm. But if we were just to call it a “G” hook, depending on what brand hook you purchased here in the US, it could be a 4 mm or a 4.25 mm.

I decided to do some extensive research online. I looked up some of the more commonly used hook brands here in the US. Many would state both the metric and the US sizes. I started to compile information on what the millimeter size of the hook was and what the letter was that it was assigned. I tried my best to be as thorough as possible. I used the information I complied and turned it into a chart that you can use as a reference between metric and US hook sizes.

The best way to check if the yarn you want to use will work for the pattern you are using is to make a gauge swatch. You especially want to do this when you are making anything you wear, like hats, gloves, or sweaters. If a blanket turns out a few inches bigger it might not be as big a deal, but when it comes to clothing, it really is. I always make a gauge swatch.