The characteristics of volume-averaged plasma density on axial propagation for atmospheric argon (Ar) plasma bullets are experimentally investigated. The non-thermal plasma bullets are ejected through a glass tube into the surrounding ambient air. Taking into consideration the time and space profile of the plasma movement, the plasma propagation is measured using a Rogowski coil. The plasma density is evaluated from the propagation velocity and the current magnitude. The plasma density profiles are presented as functions of the applied voltage and the length of growth. The plasma density is in the order of 10(16) m(-3) and the propagation velocity is in the order of 10(5) m s(-1). These values are similar to those of weakly ionized non-thermal plasma jets.