Using the Premiere pro CC 2014 exported media file size is much larger than estimate, also is so much bigger than Premiere CS 6?

I used the preset H,264 Youtube 1080HD to export a video. The estimate size is 7308 MB {after I reduce the nitrate). The final size is 11.18 GB.

Why is so much different? Befor I Use the Premiere CS6 to export a simial size use the same format Is around 6GB.