The average human arm measures 25 inches in length. However, because 25 inches is the norm for a young guy of average height and health, the length varies.
Human arm length varies as much as average human height. It is well known that there is a link between the two; taller people are more likely to have longer arms than shorter people. Children have longer arms as they grow in compared to adults of the same height, so this relationship is a little different in children. Assuming the youngster hasn’t yet attained maximum height, a 5-foot-tall child will have slightly longer arms than a 5-foot-tall adult.