`"C"_"Max" = 21 1/4 "inches"`

21.25

This constant represents the NCAA's maximum circumference of a football and is defined to be no greater than `21 1/4` inches.¹

Since we can approximate the football with an ellipsoid, the circumference through the plane of the `"axis"_1' and `"axis"_2' is related to `b` or `c` as:  `C = pi * (2 * b)`

See also

• Ohio State vs Michigan Scores
• Football Calculator
• Aerodynamic Torque on a Football
• Deflection Due to Magnus Force
• Drag Force on a Football
• College Football Consensus National Champions Data
• Most College Championships
• Number of College Football Championships
• Goal Post Cross-bar Height (American Football)
• Length of Football Field
• Sport Ball Sizes
• Minimum Football Circumference - NCAA
• Minimum Football Length - NCAA
• Maximum Football Circumference - NCAA
• Maximum Football Length - NCAA
• Minimum Football axis_1 or axis_2 - NCAA
• Maximum Football axis_1 or axis_2 - NCAA

1. ^ 2015 NCAA Football Rules and Interpretations