Once you've settled on the kind of paper you want, you have to pick the size. In the silver-halide darkroom the four most popular sheet sizes were 5x7, 8x10, 11x14, and 16x20. But because inkjet printer companies got their start making office machines, inkjet photo paper comes in workaday sizes such as letter and legal -- designated with a baffling system of letter and number combinations. (In fact, the traditional 5x7, 11x14, and 16x20 sizes have been lost in transition.) Here's some help translating U.S. and metric inkjet paper designations into old-fashioned inches.