Choosing the right-sized flat invitation cards for your event is necessary as the size should match the event! It doesn’t make sense to send out a small-sized invite for a momentous event like a wedding, neither does it makes sense to invite people with a larger-sized card when throwing a private and intimate dinner. There are certain standard invitation card sizes that can be adhered to as a general rule. 4.25" x 5.5” – Small sizes used for RSVP cards and come paired with another bigger invitation. Used for formal dinners, award ceremonies, weddings, and such. 5" x 7” – Most common standard size for Invitation Cards. Used for birthdays, holidays, and graduation parties. 6” x 6” – Big sizes used for momentous events like weddings, anniversaries, achievement awards, and important corporate functions.