Question: what size are professional footballs?
Answer: The size of a football is roughly 22 cm (8.66 inches) in diameter for a regulation size 5 ball. Rules state that a size 5 ball must be 68 to 70 cm (27 to 28 in) in circumference. Averaging that to 69 cm (27 in) and then dividing by π gives about 22 cm (8.7 in) for a diameter.