Okay, I'm confused by this...
I have 7 hi-def (720p) video captures in MP4 format that take up 19.3 GB on my hard drive. I imported them into PRE9, did some basic scene trimming, added some scene menus, and attempted to burn to Blu-Ray.
But it said that I needed 49 GB of Blu-Ray space. Huh?
Yes, PRE9 gives me the checkbox option of making it fit (ie. into 23 GB) which I assume involves some lossy compression, but I'm confused.... why the 2.5x space increase?
When you're going from one format to another -- particularly when you're working with compressed formats like MP4s, MPEGs and VOBs -- file sizes change pretty drastically from format to format.
You don't say what type of camcorder your video is coming from, what the duration of your video project is or which project setting you selected when you started your Premiere Elements project, so it's impossible to speak more specifically to your situation.
But certainly it's possible that a 20 gig source video in one format could produce a 50 gig video when converted to another.