Ampere Turns is one of the factors that provides an efficient solenoid. The ampere-turn (AT) is the unit of magnetomotive force, represented by a direct current of one ampere flowing in a single-turn loop in a vacuum.

Example: The ampere-turns for a coil with 1000 turns and a 500 mA current.
N = 1000 turns and I = 500 mA
N = 1000 turns and I = 0.5
NI = 1000 x 0.5
= 5 At
*Magnetomotive force is any physical cause that produces magnet flux.