Pixel size is 1.4 microns vs 1.75 of the N8, hence why we need larger aperture and greater sensor sensitivity to balance out the performance differential.

1.4 microns X 3552 = 4.97 mm
1.4 microns X 2448 = 3.42 mm
So the area is 17 mm.
This is just less than 1/3".. So may be 1/3.02" as against to N8's 1/1.83"