When the chairs are pulled out from the table to be used all of the legs should remain on your dining room area rug which means your rug needs to be big enough to accommodate a space larger than the footprint of your table with the chairs pushed in. A good rule for this is to seek out an area rug for your dining room that is at least four feet wider and longer than the footprint of your dining set.
An area rug is often the defining feature of a room and with this in mind should be selected with care. The rug you choose will set the tone for the overall feel of the space and will be the factor that ties in all of the different components of the décor. If you have a large space that is divided into more than one area of use rugs can bring these spaces together as a harmonious whole or can be used to further define the different regions of the room to give the feel of separate living areas.
Know what room you want it to be positioned so as to know a rug's function; whether it stands as a mere floor covering or a wall décor. Pondering on a rug's function will allow you to consider the material of the rug. For rooms with heavy foot traffic like living rooms and dining areas choose a rug that is made with fibers that are resilient to dirt and stains; specifically natural fibers like wool. If you wish to use an area rug as a wall décor (like tapestries) choose rugs made of natural silk; since silk tends to last better than other natural materials because of its delicate and lustrous quality.