What is the length and breadth of ONLY the screen in the Nexus 7?
You can always use some mathematics to obtain screen size:

X = sqrt ( Z^2 / (1 + (VR/HR)^2) )


where:


  sqrt = Square Root √‾‾‾
  
  X = screen width
  
  Z = diagonal screen size (7" for Nexus 7)
  
  VR = vertical resolution
  
  HR = horizontal resolution


which for Nexus 7, we have:

Z = 7"
VR = 1280
HR = 800


so:


  X = sqrt ( 49 / 3.56)
  
  X = 3.71 inches ~ 94mm
  
  Y = (1280/800) * X = 1.6X
  
  Y = 5.936 inches ~ 151mm


so we have 151mm x 94mm which Peanut has linked to.