I read somewhere on a forum today that someone wrote 'It may be because you are using mental ray it uses its own flags for dimensions' - whatever that means.

I am using mental ray with physical sun and sky. One of the main possible factors I have come across whilst (thoroughly) scouring the internet for this issue: THE PROBLEM: I obviously want my image to match what I typed in the render options, but it ends up being a heap smaller so I always use A4 sizing, as that's the only one big enough to see detail and go on screen (This is a problem because it takes so much longer to render & although clients usually have to downsize it, but it's better than a dirty pixellated image, right?) Down the bottom, the little white text that displays the stats of the render ( image size etc) is ALWAYS smaller than what I want it to be! I will hit render (for example, a single frame) I will type these dimensions in, along with the resolution of 72DPI (I believe that anything above that is usually only needed for print, not screen/digital) HOWEVER, for as long as I remember, I have had a problem. Whenever I want to render out a large image (or batch render a series of images) for a large HD screen (usually 1920x1080), I would think that you would simply type in these dimensions in the two fields that are easily found in the render settings. I am new to this forum so please go easy if this is a question you may have already come across which has already been answered, however this is a problem (among many in my 4+ years of using Maya) that I have been wanting to fix, particularly now that I am working full time and need to render on a day to day basis.

Arnold render settings maya 2020