The UK and US use numbered or lettered hook sizes in their patterns rather than a standardized measurement. What are the conversions between the hook sizes depending on whether I'm using US or UK patterns?
For hook sizes, it's always best to refer to the size of the hook in mm, if possible. This should be standard across all countries. Metric sizes are used in many countries including Australia and New Zealand. UK sizes are generally used in the UK and Canada. US sizes are generally used only in the US.
The equivalents (when applicable) are below. Note that some sites give different size conversions for the same hook and not all mm sizes are available in every system, which is why some sizes are listed under more than one mm size.
Crochet Hook Conversions:
There are smaller crochet hooks as well, and they have a different numbering system. These are often called Steel Crochet Hooks, and are the type of hooks you'd use with crochet thread.
|2.25 mm||2||1 1/2|
|2.00 mm||4||2 1/2|
|1.80 mm||6||3 1/2|
|1.50 mm||8||4 1/2|
|1.30 mm||10||5 1/2|
|1.00 mm||12||6 1/2|
Source: Crochet Hook Size Chart
Please note that in Canada metric sizing is the predominant measurement used for crochet hooks; i.e. 1.00mm, 1.30mm, 3.00mm, 4.25mm, 5.00mm, 6.50mm etc. Very rarely these days is the U.K. system used in Canada.
Certainly, it would be less confusing and more helpful if the metric system were for crochet hooks around the world. It is already used in many areas. Hooks smaller than 2.00mm are made by a variety of manufacturers in full steel and steel with ergonomically made handles by a variety of manufacturers.