You can simply calculate the size. The 1Ds MkIII is 21.1 Mpixels. In a 16 bits TIFF, each pixel is 16 bits per color and has 3 colors, so each pixel is 3x 16 bits = 48 bits. That's 6 bytes per pixel. Consequently, the size of 21.1 Mpixels is 21,100,000 x 6 bytes = 126,600,000 bytes. That's 120.74 MBytes.