There are two windings in Transformer one is called primary winding and second is called secondary winding. Primary winding have N1 number of turns and secondary winding have N2 number of turns.
The ratio of secondary number of turns N2 and primary number of turns N1 is called as transformation ratio. Transformation ratio is denoted by K.
Mathematically transformation ratio is given by,
Transformation ratio (K) = N2/N1