Cards are often created by laying differing sizes of cardstock or patterned paper onto the base card.
For example, start with an A2 card that measures 4 1/4 x 5 1/2 inches. You then cut a piece of card 4 x 5 1/4 inches and layer on top. You may then layer a second piece that measures 3 3/4 x 5 inches. Here are a couple of examples:
Here is a link to a document that provides measurements in quarters and eighths.