Dining room rug sizes will vary depending on the size of your room and the size of your dining table. A round 6-person dining table will of course have a smaller rug placed underneath than a 12-person rectangular table. Whatever size dining set you have, the rug should be placed so that all chair legs sit on the rug even when the chairs are pulled out from the table, and guests are seated. Typically for a 10-person dining set, a 10x14 rug would work best but depending on the room size and scale you could go larger or smaller.