The volume measurements on the Twist Pouches are very accurate (within approximately 5%) when they are read correctly. These graduations are meant to be read when the pouches are fully expanded.
To expand the pouches, pull the front and back panels apart near the base of the pouch. This will open the bottom panel. Pushing up on the bottom panel with your finger can help fully expand the pouch. It is easiest to expand the pouch once there is milk inside.