Resulting Video_TS is bigger than target filesize and cant fit on dvd?

[Rebelatheart]

I just got finished encoding a 173min avi to dvd using ffmpeg x. I used the ffmpeg encoder, and left everything as is. The bitrate was the standard 4000 kbits, to fit on 1 cd of 4gb, and then under that it had the 4000mb. When i went to burn the Video_ts folder i got the error by toast saying it was too big. It was actually 4.52gb. What did i do wrong or what do i have to change? The target filesize was 4000mb and it was suppose to fit on a 4gb dvd so i dont see why it ended up bigger. Would choosing "best" bitrate from the bitrate calculator which lowered to bitrate to 2994 kbit/s make the filesize smaller?

[Case]

The Bitrate calculator is just that: a calculator. Until you press a button, nothing is calculated.
Hover the mouse pointer over the buttons to get tool tips of what they calculate.

Changing the bitrate from 4000 to 2994 would make the final size smaller.