Turns Ratio:

Every winding of a transformer holds a certain number of turns of wire.  The turn's ratio is described as the ratio of turns of wire in the primary winding to the number of turns of wire in the secondary winding.  Turns ratio could be expressed using Equation (13-1).

Turns ratio    = N_P/ N_S                                                                 (13-1)

where

N_P   = number of turns on the primary coil

N_S   = number of turns on the secondary coil

The coil of a transformer which is energized from an AC source is known as the primary winding (coil) and the coil which delivers this AC to the load is known as the secondary winding (coil).