The Bay covers somewhere between 400 and 1,600 square miles ( 1,040 to 4,160 square kilometres ) , depending on which sub-bays ( such as San Pablo Bay ) , estuaries , wetlands , and so on are included in the measurement . The Bay covers somewhere between 400 and 1,600 square miles ( 1,040 to 4,160 square kilometers ) , depending on which sub-bays ( such as San Pablo Bay ) , estuaries , wetlands , and so on are included in the measurement .