Quick guide all about yarn weight and its different categories that includes a Free Printable Yarn Conversion Chart from Crafting Happiness.
Yarn Weight, Knitting Needle and Crochet Hook Conversion Charts for USA, UK and Australia
Determining Yarn Weights with Wraps Per Inch
A Beginner's Guide to Yarn Weights
Crochet Techniques collection - Crafting Happiness
Crochet Techniques collection - Crafting Happiness
UK vs. US Knitting Terms, Yarn Weights and Needle Sizes - Little Red Window