The sanding-pad size affects the surface area covered, the level of control, and the applications the tool is best suited for.
A 3" random orbital sander provides greater control for spot sanding, trim, refinishing, and smaller surfaces. A 5" random orbital sander is a versatile size for woodworking, renovation, and general surface preparation. A 6" random orbital sander covers a larger area and is commonly used for automotive body and paint applications.