SPACE SURROUNDING DINING TABLE
Comfortable dining table proportions allow enough surrounding room for maneuvering around the table and its accompanying dining chairs. Ideally, a minimum of 36 inches of surrounding space will meet both these requirements well. These proportions obviously become more important for a small dining space, so be sure to take the measuring tape out before splurging on that favorite dining table, no matter how perfectly suited to your space it may look. Eyes can be deceiving.
SPACE BETWEEN SEATING
In most cases, it will be clear how many people a dining table can comfortably seat, which is to say, how many people can sit and eat without touching elbows. That doesn't mean that more people can't be accommodated, of course, but it's useful to remember that each person should be given about 2 feet of space in which to eat comfortably. So if you're considering adding an extra seat (say, for a round table), either permanently or temporarily, keep that 2 feet measurement in mind. There may be occasions that necessitate less-than-ideal space for eating, but a comfortable seating distance should be the rule, not the exception.
DINING TABLE WIDTH
Dining table widths are commensurate with table sizes, of course, but the minimum dining table width for place settings as well as serving pieces, is 3 feet. If space is an issue, you can go narrower, with the tradeoff being that not much more than place settings will make it to the table.