How do you convert using MPEG Streamclip?

I'm trying to convert a file for editing in Final Cut Pro X using MPEG Streamclip. I followed the instructions in a tutorial, which was to set the output as Apple ProRes 422 LT and the pixel dimensions at 1920x1080(unscaled). After I converted it this is the file info I got for the new converted file when I hit Command+I in QuickTime

FPS: 29.92
Data size: 22.71 GB
Data Rate: 69.92 mbit
Current size: 1440x810 pixels

WTF? Are the dimensions I picked totally wrong? How did it swell to 22 GB? And it wouldn't even play in Final Cut anyways.

I must be missing something obvious, but I am having the hardest time just converting a simple file so I can edit it.