There are several issues to consider when choosing a light to be placed above a dining table:
- Width of the table
- Height of the ceiling
- Style of the table
Width
The purpose of the dining table chandelier is to light the tabletop. A general rule of thumb is to size the chandelier approximately half the width of the table, though this is flexible depending upon the overall feel of the room. I have seen dining rooms that appear quite spacious and grand with a lengthy, but slightly narrow table. The chandelier above a table such as this could be slightly wider than half the table width, especially if the ceiling is higher than eight feet. With this extra width, the light will fit the scale of the room.
Height
The bottom of the chandelier should hang 30 inches off the table top on an 8 foot ceiling. The higher the ceiling, the higher the fixture should hang, adding two to three inches for each extra foot of ceiling height. If you have tall family members you may want it to hang a little higher. The test is to sit in a dining chair at the table, then push back and stand up. Notice that your head goes forward.
A difficult part of the selection process for most buyers is determining how close the fixture may hang to the ceiling. I like to see eight to ten inches of chain and canopy. Remember that stated measurements on new fixtures include the “hanging ring” to which the chain is attached. Some interior designers do not like to see much chain at all and will hang a fixture with only one or two links. When you are looking at fixture heights just remember that the canopy and the attached ring usually occupy two to three inches of length and you need one link to hang the fixture.
Table Style
A heavy, bulky style table can handle a heavy, bulky looking chandelier and a light and airy glass top table could use a slightly larger open-air style chandelier. A long table can use two or more chandeliers or pendant style fixtures. Many customers in our lighting showrooms are using outdoor lanterns over tables, especially over the longer farmhouse house style tables. My advice is to first find the one that gives you the WOW feeling and then see if it will work.
Other Sources
According to the Hinkley Lighting Guide:

To size a chandelier for your dining room or bedroom, you’ll need to measure the length and width of the room and add those figures together. The sum, converted to inches, will equal the diameter of the correct size chandelier. In the dining room, if this measurement seems inappropriate due to the size of your table, size your chandelier three quarters the width of the table. The bottom of the chandelier should be approximately 30-32 inches above the table top.
Written by: Karen Long, ALA Lighting Specialist, ButlerLighting.com