Disclaimer: I am the product manager for Ambu Inc. I'm not sure if this is in line with the forum, I apologize if not.
However, I saw this when doing a search and thought I would answer for our company.
Our total volume for the Ambu Spur II disposable resuscitator is 1475 ml. However the previous poster is correct, a lot of the other manufacturer's bags are 2 liters in total volume. A one hand squeeze with our resuscitator gives 800 ml. A two handed compression, which is not recommended, will give 1100 ml.
As I'm sure you know, the AHA guidelines for resuscitation suggest that the ideal volume is 500-600 ml. However the extra volume in the resuscitator allows for a small leak around the face mask which is common.