At least 3 feet larger on all 4 sides so that when you push a chair out, the legs won't catch on the rug....
...so for you, you'd need a 12'x10' rug.

Yikes...that's not an easy size to find! Thanks for the input!

Actually, you could easily go to your local carpet retailer and select a remnant or off the roll of Wall-to-Wall and have it cut & bound in the size you need...
...and if you want something even more special, they can do inlays, contrasting edging, etc.

I have an 8x10 foot rug under my table that is 44 x 79 and it works fine

I guess the size of the room is something to consider too. Thanks!