The formula used can be found in Quora.com (population*average height)/Earth's circumference), gives the result of the number of the human chain.
If the average height of an American is 1.77m and the US population is 326, 292, 068 (June 2, 2017) and if everyone is already an adult.
US population 326, 292, 068
Average height according to study
is estimated as the same as arm span 1.77
Earth circumference in meters: 40,075,000
(326, 292, 068 people * 1.77m) / 40,075,000m = 14.411 times