You also have to take in to account the height of your ceiling, the size of the room , and whether the fixture is to be a focal point in the room.
On an eight foot ceiling, the pendant may be too large, but on a higher ceiling it may be just right.

It is an 8' ceiling, but it's part of a large open living area and the only ceiling pendant/focal point of the room. Do you think the table:lamp diameter ratio is awkward?

We've been working with a lighting designer in SF, and he is adamantly opposed to overscaled lighting (just his opinion, of course). We will have 9.5' ceilings in the dining room, and our table will be approx 75" square. He won't "let" us go over about 40" diameter so that no one will feel like they'll hit their head on the fixture when they stand up (even if it's actually hanging too high for that to actually happen), and so the scale will look appropriate.

At 40" dia, we will have about 17 horizontal inches between each diner and the rim of the chandelier (75/2 = 37.5, minus 40/2 = 20 = 17.5"). In his mind, that's about right.

Hope that helps.....

I think that you show be looking for a fixture that is 28"-32" in diameter when hanging off an 8' ceiling.
It should be hung with the light bulbs just above standing eye-level of the tallest person in the household.

As a general rule--and the operative word here is "general"--the fixture should be about 12" less than the width or diameter of table. The idea of course is with the fixture centered more toward the center of the table, then even the tallest of guests should be able to sit and stand without hitting their heads on the fixture.

Of course there is the old rebellious adage "rules are made for breaking." So it comes now to a personal comfort thing--how comfortable will you and your guests feel sitting at a table with an over-scaled light fixture? My experience is most people are not comfortable with oversized anything--we prefer things to human scale.