Actually the Canon APS-C sensor is 38.5% the area of the FF sensor.
APC-S: 22.3 x 14.9mm = 332.27 sq/mm
FF: 36 x 24mm=864 sq/mm
In other words, the FF sensor is 2.6 times larger than the crop sensor.
Yupp, the laws of geometry are old but still quite magical for many people When I have my Mamiya 6 with me and people ask me why I use this strange camera that looks like a Leica on steroids, they are always stunned when I explain them that the size of its film negatives/positives is about four times as large as a 35mm frame.