For business cards specifically there are two common sizes in North America. The first is 2′x3.5′. This is the standard size business card you will find in every print shop down the street and all the online vendors.

The second most common business card size in North America is 4′x3.5′. It is commonly called a ‘folded business card’ and looks a lot like a table tent in a restaurant.

Many printers will also do custom cuts for you if you are willing to pay for it.