Bear in mind that if you set a maximum image width and height then the image will be resized automatically. This is a much more user friendly way of controlling the disk space used.
As a very general example (e.g. with one image I have on my machine right now), let's say you accepted file sizes of around 2.1MB this would be approximately 4064px x 2704px resolution. If you set your max width/height to 1280 x 1280 then this image would be resized to approx 1280 × 851 automatically.
The resulting file size is 350KB and your end user hasn't even had to worry about having to resize images beforehand.