Fujifilm GFX 100 has a Medium format sensor with dimensions of 44 x 33 mm and sensor area of 1452.00mm2.
Fujifilm GFX 100's sensor is 277% larger than the average Mirrorless sensor in its class. In cases where all the other parameters are the same between two cameras, the one with the larger sensor collects more light per pixel and performs better (less noise) in low light / High ISO conditions . Larger sensors also give the photographer more control on the depth of field.
Read our detailed Fujifilm GFX 100 Review