I just had to share this chart that I found (both in US and UK crochet terms) for figuring out how to make different shapes, like circles, squares, triangles, and hexagons, in crochet! I really like how user-friendly it is, laid out very nicely.
I found it during a search for a formula for shawl making. I've been working on creating a shawlette pattern and have been getting frustrated because, frankly, I've just been winging it when making each row rather than figuring out mathematically how many stitches I need on each row in order for the shawl to "grow" into the shape I want. Let's face it, crochet (and knitting too) involve math, there's just no way around it if you want an accurate and well-shaped crocheted item. It's worth doing some up front planning because you're just going to get frustrated and end up wasting time along the way (and still end up going back to making calculations :-)
So, back to the drawing board!