For all my lack of skills, I adore the tools of crafting. Petals to Picots has a wonderful and brilliant conversion for hook and needle sizes, lengths, weights and recommended needle/hook sizes for projects in both metric and US gauges.
I am in love. So many of the bloggers I follow are from Britain, and are using metric measures and hooks. They almost always convert for you as they write, but how nice to have the information all in one chart.