The most traditional size for a wedding invitation is a 4.5 inch by 6.25 inch rectangular card. Most of the time wedding invitations aren't much bigger than a 5 inch by 7 inch design. If it's too big it will look silly, but if it's too small it might be hard to read. Nowadays there are lots of creative designs for wedding invitations like circular scalloped, oval, or other unique shapes that all come in reasonable sizes and add flair to your wedding invitation.