If you wanted to, you could take newspaper and lay them on the floor to the size of your table. Then add another newspaper for each chair. That will give you some idea of the "footprint" of your table. Your room is 12 feet long and your table is 7 feet long..if your table is in the center of the room, you will have 1-1/2 feet on each end of your table.

We now have a small dining room, just over 11' wide x 14'. Our table in 43" and there's not really enough room for food plus flowers, candles and place settings. I wouldn't reduce to 36" if you like to have the convenience of serving dishes on the table.

Eighty inches seems too long for your room, but then I like plenty of space for people to walk behind the diners when they are seated. I add four feet to each side of the table's measurements. So, in your case, the table length of approximately 6.5 feet plus 8 feet (4 for each end) yields a dining room length of 14.5 feet. For the width, use the 3.5 feet plus 8 feet for 11.5 feet. Without any china cabinet in the room, that seems reasonable. Of course, it's completely up to you and your comfort level.

Thanks for the responses..I still don't know what to do - keep the set I have on order or look for something a bit smaller in length but stay at 38 to 40 wide. The set is a very dark mocha, so the color may even make it look bigger.
Gex, the one room I thought I had a handle on - I may need to start over on...

If you have a china cupboard that will be on one of the 12 foot walls, and it is no more than 20" deep, you can fit the table into the room, but the person at the end of the table adjacent to the family room, may need to push the chair back into the entry way between dining a family room to get up from the table.

Arithmetic:

80" long table = 6' 8".
Recommended chair space = 3' (36") x 2 chairs = 6'
Table + chair space = 12' 8"
Room length = 12'

40" wide table = 3' 4"
Table + chair space = 9' 4"
Room width = 11'
Maximum depth for china cupboard = 1' 8" = 20"