Each class of airspace has its own minimum visibility and cloud clearance requirements for flight under the visual flight rules, designed to allow pilots adequate opportunity to see and avoid each other. These rules are found in FAR 91.155.
Class A (Class A, NA)
Minimum visibility and cloud clearance requirements are not applicable to Class A airspace, since flight under VFR is not permitted.
Class B (3 and Clear)
Visibility must be at least three statute miles. There is no minimum distance from clouds which must be maintained. The airplane must simply be operated so as to remain clear of clouds.
Class C (3 Cessna 152's)
Visibility must be at least three statute miles. A distance of 1000 feet above, 500 feet below, and 2000 feet horizontally must be maintained from clouds.
Class D (3 152's)
Visibility must be at least three statute miles. A distance of 1000 feet above, 500 feet below, and 2000 feet horizontally must be maintained from clouds.
Class E Above and Including 10,000 Feet MSL (5 F-111's)
At altitudes at or above 10,000 feet MSL in Class E airspace, visibility must be at least five statute miles. A distance of 1000 feet above, 1000 feet below, and 1 statute mile horizontally must be maintained from clouds.
Class E Below 10,000 Feet MSL (3 152's)
At altitudes below 10,000 feet MSL in Class E airspace, visibility must be at least three statute miles. A distance of 1000 feet above, 500 feet below, and 2000 feet horizontally must be maintained from clouds.
Class G At Night
During the night, Class G weather minimums are the same as Class E weather minimums. They are still five F-111's at or above 10,000 feet MSL, and 3 152's below 10,000 feet MSL.
Class G During the Daytime
During the daytime, Class G weather minimums are still the same if at or above 10,000 feet MSL, five F-111's.
Below 10,000 feet MSL, however, the weather minimums are more relaxed than the requirements of Class E airspace. Only 1 statute mile is required instead of three. VFR weather minimums are 1 statute mile visibility, with cloud clearance requirements of 1000 feet above, 500 feet below, and 2000 feet horizontally.
Below 10,000 feet MSL and also below 1,200 feet AGL, the weather is further relaxed to allow VFR flight clear of clouds. VFR weather minimums are 1 statute mile and clear of clouds.
ยง 91.155 Basic VFR weather minimums.