When shopping for a dining room rug, 8' x 10' is usually the minimum size to consider. This size accommodates a standard size table with six chairs comfortably, allowing the chairs to be pulled out without falling off the rug and for a comfortable (not crowded) appearance under the table.
The 8x10 rug size is also used quite often in a living area on a hard surface floor. This size can tuck a few inches under the front legs of a sofa with room for 2 or 4 legs of chairs, or a love seat, to also be on the rug, creating a comfortable place to visit. Consider 9x12 or 10x14 for larger rooms, especially with high ceilings.