What is the optimal video file size for uploading?

A 3-minute video file should be less than 300 MB in size.  If you have a choice, do not make your video in high definition format.  Choose an “export” setting such as “medium,” e.g. 640/360 pixels, rather than “large”, e.g. 960X540.  If your video file is larger than 300 MB, you should compress your video file (see How do I compress my Submission?).