There are no 6×6 sensors, the largest we’ve got is 53.7×40.2mm (Hasselblad H5D-60) which is still a bit smaller than 645 format on 120 film.
This sensor’s dimensions are 43.8×32.9mm, it’s the same size as the CCD used in the old Pentax 645D and it’s actually smaller than the CCD in the Hasselblad H5D-50 (49.1×36.8mm).
H5D-50c: 43.8×32.9mm (crop: 0.79, 1.67x larger than FF)
H5D-60: 53.7×40.2mm (crop: 0.65, 2.5x larger than FF)
645(film): 56×41.5mm (crop: 0.62, 2.69x larger than FF)
6×6(film): 56x56mm (crop: 0.55, 3.63x larger than FF)
6×7(film): 70x56mm (crop: 0.48, 4.54x larger than FF)
6×9(film): 84x56mm (crop: 0.43, 5.44x larger than FF)
Started out doing photography at the age of 6 using an uncle's old 1940 kodak brownie box camera. At 15 years of age, I decided to buy my very own 1975 Praktica SLR camera. I now shoot with a Nikon D850. I do unpaid TFP and commercial paid work.