Generally, the arm circumference of normal boys who don't exercise is around 28, that of men who often do manual labor is around 30, that of men who often exercise is around 35, and some people can even reach 40.

The arm circumference reflects the degree of development of arm muscles. Upper arm circumference includes upper arm tension circumference and upper arm relaxation circumference. The average difference in arm circumference is 2-3.5cm for males and 0/.5-2 cm for females. Measure the thickest part of the upper arm with a tape measure.

Maximum circumference of upper arm

Maximum circumference of biceps brachii: when biceps brachii contracts, the circumference of the section perpendicular to the axis of the upper arm where biceps brachii expands the most.