Knitting needle sizes
I don’t know about you, but I'm always finding that I need to know what size a needle really is, and end up spending a bunch of time looking for a needle size conversion chart. Since I'm more familiar with the U.S. sizes, those are first in the list, followed by metric sizes, U.K./Canadian sizes, and ending with Japanese sizes. I also have a chart of crochet hook sizes, if you need to take a look at that, too.
Another thing people often want to know is what length circular needle they should use for a given project. The following chart shows the minimum number of stitches that will realistically fit on a given length needle. What's the maximum number of stitches that will fit? However many you're comfortable with. Truly. I've crammed hundreds of stitches onto relatively short circulars many times, as my longer ones are already busy, or I'm too lazy to make the change. So long as your stitches aren't falling off the needles you're good to go.