Do you ever feel frustrated when looking for a matching thread? Maybe your project instructions call for one brand of floss but you can only find a different one. Perhaps you have a lovely skein of overdue and you want to know solid colors that match.
The tool you need to do this is a conversion chart. While they are not perfect (you should check the threads with each other), they will help you find the answers you need.
The Truce has put together a great article on conversion charts, with links to ten of the best.
Keep in mind that this article is for cross stitchers, so it is heavily weighted towards floss. Also remember that for several of these companies the color numbers are the same for pearl cotton as for floss.