The size of the medallion is determined by three factors: the size of the chandelier, the size of the room and the height of the room. Medallions were created to be fire barriers and must always be larger than the chandelier lights. This has created an historic precedence for sizing. Thus a good rule of design is about 40% larger than the chandelier diameter. This 40% is also a good rule as the medallion looks much larger in hand than it does on the ceiling due to the distance from your eyes.
