TNT explosions have a 3'3'3 area, instead of regular "messy/random" TNT explosions

hint: shouldnt give measurements in feet when blocks are in meeters (i.e. 3'x3'x3' is 1 block,roughly)

Besides that if your refering to a 3x3x3 block cube with tnt in the middle then, thats going to happen... Maybe you should attach a screen shot or two of the setup so we can try and reproduce.

The wiki describes the force of TNT explosions (http://www.minecraftwiki.net/wiki/Tnt ):

The TNT blast will propagate according to the formula f=e-r, where f is the force of the TNT blast after propagating through the block, e is the energy of the blast before propagating through the block, and r is the blast resistance of the block. Thus, the explosion propagates farthest (7 blocks) through air, which has a blast resistance of zero. However, TNT immediately enclosed in stone will destroy an exact 3x3x3 cube originating from the center of the blast. The damage is usually lethal at close range.

that site is blank

sorry... they changed the page name and somehow I copied the wrong one

http://minecraft.gamepedia.com/TNT

I just uploaded a screenshot of a TNT test. I used 5x5x5 cubes of End Stone and Stained Clay, and a 9x9x1 wall of Glass.
Despite the difference in blast resistance, the End stone and Clay both had the same 3x3x3 explosive cube. I cut away the foremost layer so you could see.