How do you choose the best width for your pendant shade?   Here are some general rules of thumb:

If the pendant will be hanging in the center of a room, measure the diagonal length of that room from one corner to another.  For the best proportions, the width of the shade in inches should be equal to the diagonal length of the room in feet.

If the pendant will be hanging over a table, choose a shade width that is at least 12 inches less than the width of the table.

Color matters. If the color of the shade matches the walls, choose a slightly larger shade so that it has enough visual substance. If the color contrasts with the walls, choose a slightly smaller shade so it is not overpowering.