Why are there more sq feet in a 30 x 30 area than in a 24 x 36 ares?

[Tor]

Ya ya I know how to multiply; 30 x 30 =900 and 24 x 36= 864. But when it comes to housing space (I'm drawing a housing plan) if you take a 24 x 36 space ( take 6 feet from one side and add it to the other it should be the same sq footage as the 30 x 30 right? I dont understand and its messing up my drawing because I cant fit as much in that space.

[JARED]

You multiplied it out and you see that the 24X36 space is 36 square feet less than then 30X30 space. The perimeter is the same, but the area is not.