I would make the runner long enough so that it looks correct for the size of the table you normally us. I don't think it will look all their weird if the runner is partially under the place mats, or you could just fold the ends under so that the runner ends short of the place mats. People will be concentrating on the food and the conversation anyway. This is not a life or death issue, just relax about it.

I guess it depends on how thick the fabric is that you're using. I wouldn't want a runner under my place mat if it is going to make my plate uneven - sort of like a wobbly table, which you don't want.

Thanks! LOL! I'm not stressed... just confused. And I overthink everything, so I'm easily confused :D blfenton - that's exactly what I was thinking... since I want it to be insulated to protect the table from heat, it will be a thicker fabric, and I'm thinking it might make the plate wobbly. We are usually paper-plate-casual-chaos for our holiday dinners, but I want to make it nice this year! I've seen lots of pictures where it's just in the center of the table. I was originally thinking I wanted something more elegant, but I think maybe I'll just make it 60" long...then there's room for placemats at the ends of the table when it's extended as well as when it's the usual size. Waddya think?

I think that plan sounds good! Are you making a quilted runner, like what is in your photos?

Bluebell - thanks!! I may try quilted on one side. I found a tutorial online for a reversible option and I have a friend who is going to help. She knows what she's doing...but I don't, so we shall see lol!!

My table is big too and some of my runners are pretty long and some are shorter. DH and I usually sit at the ends when we have guests, so I just let it hang where it may and deal with it. Maybe that sounds bad, but really it doesn't matter. I seldom use my runners actually during a meal because I put the table pads and a cloth on the table with a centerpiece and other serving items. No room for wine glasses, water glasses and other things without a disaster due to the uneven-ness in height of a runner in the way.

Our dining room table is 9 1/2 feet long and I never use any runner longer than 5 feet on it. Like others here, I don't like to have it hanging in the laps of my guests, although during our dinner parties, it's my husband and I who sit at each end. I also don't like putting a placemat over a runner.

Goo point... I was going to make it 15" wide, but maybe I'll make it narrower to make it less likely that glasses will get set partially on it. Hmmm...but then there's the question of how to protect my table from the glasses. Usually I just put down a folded paper towel cause I'm classy like that ;) we just don't entertain. Now I'm realizing why lol!

Goo point, aka good point lol.
And I just realized the glasses will be on placemats (hopefully!) but maybe I should still make the runner narrower than 15".