Wall facing door: (69.5" x 56.75" minus door) = 18.37 square feet. 
Wall behind sink and toilet: (68.75" x 57") = 27.21 square feet.
Wall Opposite Door Wall: (70" x 57") = 27.71 square feet.
Wall Opposite Sink: (68.5" x 57") = 27.11 square feet. 