The 2009 A4 is more spacious then all 3 of its closest competitors; the BMW 328xi, Mercedes C300 and the Lexus IS250. This roomieness is not just achieved in head, shoulder or leg room but is superior in all three.
This chart can be used to see the exact interior capacity in inches.
Here is a side by side comparison of the side and top view of the 2009 A4 Sedan. As you can see the overall length has been increased by almost four inches and the wheel base has been increased by almost 6 inches from the 2008 Audi A4.
As with the previous year, the 2008 A4 Sedan and Avant will have identicle dimensions in wheelbase and in vehicle length.
With this top view diagram of the 2009 A4 you can see where the addition two inches of width have been gained, giving you more shoulder room that ultimetly equates to safety and comfort.