The NOMATIC Vacuum Bag is the best way to pack more in less space. Using the air valve, you can compress clothes and soft goods to condense their overall volume, no vacuum needed. The Vacuum Bag also makes a great place to put wet or dirty gear while traveling to keep your other valuables clean and separate.
Here are the dimensions for the vacuum bag:
17" L X 25" W X 14" H (expanded)
The vacuum bag is about 10L and can potentially fit more, depending on how you pack.