The 26" rule applies so that if someone is sitting at the table, another person will be able to squeeze by. If you use a sideboard, that would not leave enough room for someone to pass by on that side only. To me, go the other way when passing by the table.

You have 48” table 36 + 36 on the 2 sides where the chairs are on opposite sides of the table and that leaves you 24” for a sideboard what am I missing?Just because some photographer took a picture does not make it workable. The easiest is to center the table mark off the 36” all the way around and see what is left for a sideboard, you can get a thinner one if you feel to cramped.

That is one tiny dining room!

I agree with Michael Menn, but if you had your heart set on a sideboard, this one has Dimensions:

Overall: 35 3/4"H X 39 1/2"W X 10 3/4"D

I like looking at nice photograph, don't you? :)

Thanks to all of you for your input. And of course I meant 12x12 feet ;-)

I just tried placing the chairs so that they pulled back towards the corners of the room rather than towards the walls. In that configuration, I could place a sideboard that was 50 to 60 inches long and the chairs would never touch it even if pulled out all the way. However, while there would be 28-30 inches between the table and the sideboard, it might be awkward to reach the sideboard while people are sitting in the chairs. My main concern is: would it look too cramped?