Batch less than 5 gallons - change sugar amount for bottling?

I will be bottling my honey oatmeal stout this weekend. When we took the FG reading I noticed that my original 5 gallon batch is quite a bit smaller now. We did rack into a carboy a few weeks ago and left a bunch of stuff in the bottom of the bucket. I was surprised to see how much has dropped to the bottom of the carboy. My guess is I probably have 4 gallons or less of beer. (Kind of a bummer because it has a great taste at this point.)

But, my concern is do I use less sugar for bottling now? And, if so, how do I figure out how much?

I do have BeerSmith, but I just downloaded it the other day. I don't know much about it yet, but didn't immediately find anything that would help me convert this.

Thanks in advance!

Here you go!
http://www.tastybrew.com/calculators/priming.html

Yes, I'd use less sugar. Do you have a scale? I use a small kitchen scale to weigh my priming sugar. Beersmith has the tool right in the recipe, about 3/4 of the way down on the page, but you'd have to change the batch size to four gallons.

Otherwise, http://www.brewblogger.net/index.php?page=tools&section=sugar has a priming calculator. I'd use 3 ounces (by weight) for 4 gallons of stout.

Yes. If your making a 2.5 gallon batch, and you normally prime your bottles with 5 ounces of sugar, then obviously, just like you cut all your other ingredients in half, you would use 2.5 ounces of sugar.

If using the "standard" 5 ounce/5gallons that any kits utilize, that breaks down an ounce of corn sugar for a gallon of beer. so 4 gallons, 4 ounces. Etc.

Excellent. Thanks all. I figured as much. I am pleased that I knew enough to ask the question and that I asked it before I bottled!