The rule of thumb when you do a layout for a rug as follows.... Put the table and the chairs in the room, install table extension. Pull the chairs out as if you going to sit down at the table. Use the tape and put the tape 4-6" behind the chair and that should be your rug size.

Usually, with the chair out, the back of the chair should be 24-28" away from the table and that should be your rug size. Here is an example, not sure how big your room is with a 54" round table with a 16"leaf your rug should be 11'6" X 10'5" or get one to the near size.

You want to select a rug that is sized correctly for the room, not so much the table.

IMO you need at least 36” around the whole table when the leaf is in

After reviewing all of these great comments and suggestions, and doing some more measuring I have decided that a 9x11 rug is my best option. Where is the best source for a custom size such as this?