Letter size : The size 8.5x11 in is well understand if i can say its of a company letterhead size or the size of a standard piece of paper used in xerox/photocopy. This size is useful for companies, business enterprises, and local administrations with a lot of information to share. It can be useful for school leaflets for example, and they can easily be folded, put in an envelope and sent by post.
Statement size : The statement size 5.8x8.5 in is the standard flyer size used for promotional campaigns and marketing strategies, newspaper insides etc. Flyers of this size are a convenient size for distribution too.