What size tub for small rack?

I usually see people using the medium mixing tubs for there rat racks to hold four to five rats (1.4 ratio), however I am looking to have a much smaller system. I'm only looking to house 1-2 females per tub(with the males alternating in and out) and I want to know what is a good size? As a pet rat owner as well, I tend to err on the larger size, which is defeating the purpose xD
Dimensions are all I'm really looking for, I understand that 6" is the preferred depth. I hope to get a response soon, I'm excited about building my first rack :)

Here is a link to a thread I had about a maternity rack for rats. This tub size would also work well for one maybe two female rats with their litters. Remember that a dozen nearly weaned baby rats can take up a lot of room.

http://ball-pythons.net/forums/showt...089#post550089

Thank you so much! That's exactly what I needed :)