Choosing the right needle size or crochet hook size is critical to how you project will turn out.  I often will change the size recommended by a specific pattern to make a tighter fabric or adjust the fabric for a specific yarn. Here is an example project where I adapted a pattern designed for chunky alpaca to work with a lighter weight alpaca yarn. 

The diameter of your knitting needle or crochet hook determines the size of the resulting knitted/crocheted stitches. Needles and hooks usually include both US needle sizes and metric sized (mm). However, sometimes patterns will only specify one or the other, that is were this conversion chart comes in handy. In some cases, the needle size may rub off the handle on the needle or crochet hook or it may be too small to easily see. For these reasons, we recommend keeping a needle gauge in your knitting/crochet bag.