This can vary by surgical procedure and surgeon. In a Roux-en-Y gastric bypass, the stomach pouch is created at 1 ounce or less in size (15-20 cc). In the first few months it is rather stiff due to natural surgical inflammation.
About six to 12 months after surgery, the stomach pouch can expand and will become more expandable as swelling subsides. Many patients end up with a meal capacity of 3 to 7 ounces.