Before revision: The individual rectangles that make up the system each measure 1 degree of longitude by 0.5 degrees of latitude and are intended to be roughly square in real world use ( approximately 30 nautical miles by 30 nautical miles at 60°N ) although the actual width varies with latitude, gradually becoming wider than they are high south of 60°N, and higher than they are wide further north.
After revision: The individual rectangles that make up the system each measure 1 degree of longitude by 0.5 degrees of latitude and are intended to be roughly square in real world use , approximately 30 nautical miles by 30 nautical miles at 60°N ,(55×55 km) although the actual width varies with latitude, gradually becoming wider than they are high south of 60°N, and higher than they are wide further north.