I'm more of a practical gal, so I would size the pendant by how much light I need. In my closet, I have a large fluorescent fixture because I told the electrician I wanted to be able to see the difference between black and navy...I can.

If you are looking for more decorative, then I suggest getting a plastic grocery bag and stuff it with newspaper to approximate the size of a light fixture under consideration and have someone hold it up so you can see what it looks like...

Thanks for the idea AnnieDeighnaugh. Unfortunately the closet hasn't been built yet. I'm trying to buy ahead of time.

Do you have a room or a closet of about equivalent size now so you can get an idea?

There are lighting guidelines on the net to calculate how much brightness you will need given a room size. That may help you determine the size of the fixture you will need to light the closet.

Or there's this:

For ceiling fixtures in a room:

In general, take the width and the length of the room in feet, add those two lengths together and convert to inches. That is the basic size fixture you should purchase for the space. For example, a living room that is 15â²-0â³ x 12â²-0â³ = 27â²-0â³ So your ceiling fixture should be approximately 27â³ in width. Of course, rules are meant to be broken...

Here is a link that might be useful: Lighting needed