For Dining Room
Measure the dimensions of the tabletop and add 54" to the length and width of your table. The extra 27" around the table will allow space on the rug for when chairs are pulled out from the table.
Measure your bed and add 24" to each side; this allows enough space to have the rug under and around the bed. Or choose a smaller sized rug to place beside or at the foot of the bed.
For Living Room
Furniture should be placed either entirely on or off the area rug. Measure accordingly.