Start with the table, not the fixture. Measure the tabletop width and the ceiling height, then choose a pendant that leaves clear sightlines across the table.
For a round table, a pendant diameter of about one-half to two-thirds of the table width is a practical range. A 42-inch table often suits a pendant around 21–28 inches wide. A long rectangular table can use one linear pendant or two smaller pendants spaced evenly.
Hang the bottom of the fixture about 30–36 inches above the tabletop. Use the higher end when ceilings are above 9 feet, and keep the shade above eye level when people are seated. If the canopy and cord are adjustable, confirm the minimum and maximum hanging length on the product page.
One pendant can light a smaller table. Larger tables usually look more balanced with a linear fixture or a repeated pair. The fixture should light the tabletop without blocking the view of the person opposite.