EOS 5D Mark IV: image size setting

When setting the image recording size in the Image Quality screen, you may notice the pixel dimensions and also the number of possible shots on the free space of the memory card in the camera. While shooting, and afterwards, you may notice a difference in the pixel dimensions or that you achieved substantially more images than expected. If this is the case, it is likely because you shot with an Aspect Ratio setting that is always less than the full sensor 3:2 ratio that the pixel dimensions and capacity calculations are based on – regardless of the Aspect Ratio settings you may have made elsewhere.
Camera settings
EOS 5D Mark IV