What size should I be looking for? And to be perfectly honest, often I just eyeball it. However, I know that many clients like to be more precise than that and need concrete directions on this subject.
What size do I need? If we are talking about the foyer, entryway, family room or bedroom - the easiest way to get an approximate height is to take your ceiling height and times it by 2.5. For instance, if your ceiling height is 10', you would take 10 x 2.5, which would be 25, so a light fixture about 25" tall is what you need to use as an approximate size. Really anywhere between 2.5 and 3 is good. So for 10' ceilings, a light fixture about 25" to 30" is a good place to start. Some light fixtures are very "airy" and are visually light, so in those cases you can even go on the larger size. As far as the width goes, take your room dimensions and multiply. For instance, if your room is 12' x 15' that is 12 plus 15 equals 27, so use 27" as your estimate.
What about over my kitchen table, dining room table or island? Where should I hang it? Hang your chandelier so that it's lowest point is 34"-36" from the top of the tabletop. If you want to place two smaller light fixtures over a long table or island, choose a diameter that is about one-third of the width of the table or island.
There are so many great sources and designs now. The right lighting can make a huge impact and give your room a whole new feel. It is amazing the personalities that light fixtures have these days! They are so fun! So go ahead and replace that dated light fixture.... you will be glad you did.