Choose the shape of your book based on the content you plan to put in it. The choices are:
Square – 12×12, 10×10, or 9×9 – when you have a images of various shapes a square book always works. Smaller books – 5×5 or 8×8 are also available.
Landscape – 12×10, 12×9, or 10×8 – if most of your images are horizontal this format is best.
Portrait – 9×12, 10×12, or 8×10 – suitable for weddings and memoirs with a lot of text. Miniature versions keep the same aspect ratio but are 5×6.6