UTH size for 15 qt tub?

Hey all, I tried searching a few different ways and was unable to find what I am looking for. I need to set up a QT tub and was wondering what size UTH/heat mats you would use for 6 or 15qt stand alone tubs? Also, does anyone have an opinion as to whether ZooMed or Exoterra makes a better heat mat? I plan to use my UTH with a rheostat since it will be a temporary enclosure and want to make sure I use the correct size. Anyone have any pics of small-stand alone tub set ups? Thanks so much in advance.

I use a 6"x11" Ultratherm heat pad from Reptile Basics on my 15qt tub. http://www.reptilebasics.com/ultrath...uth-6-x11.html

I like them because they are not sticky...you tape them on with aluminum tape and you can reuse them. I'll try to post a pic later.