When buying a fan ceiling fan size vs room size is an important consideration 

When looking at what fan is right for a particular room you need to take a look at ceiling fan size vs room size for the fan to do its job properly. The first step is to take the measurements of the room the ceiling fan is going in which is the width and length in feet. Once you have these measurements you then multiply them (width x length) which will give you the square footage of the room.

Once you have the square footage then here is a ceiling fan size vs room size to follow.
      
Room Size                                                         Blade Size

Rooms 100 sq. ft. or less                                     27”- 26”
(10 x 10)

Rooms 100-150 sq. ft.                                         42”-44”
(10 x 15)

Rooms 150-400sq.ft.                                           52”-54”
(20 x 20)

Rooms greater than 400sq.ft.                               56” fan or use two fans using the above
                                                                              Guide

Another consideration when taking a look at ceiling fan size vs room size is to take a look at the ceiling height. In order to install a ceiling fan there needs to be at least 7 feet of clearance under your blades. For a ceiling that is 8 feet a standard mount is usually used and a flush mount is used for ceilings under 8 feet. For higher ceilings that are 9-20 feet there are extended mounts fans that have downrods.