The output voltage of the transformer must be changed because to meet the quality of service voltage according to the needs of the consumer (PLN Distribution). To change the ratio of the turns / ratios (ratios) the transformers are made tap (tappers) on either side of the transformer. The method used in this research is to compare the result of transformer ratio measurement using TTR (Transformator Turn Ratio Test) with formula calculation result. Counter number of winding transformer serves as a counter number of transforamator secondary turns. Multiplying the number of secondary windings to the equation of the voltage ratio is equal to the ratio of the turns, then the magnitude of the primary winding calculation is obtained by Afterwards it will be calculated the number of primary winding measurements by multiplying the secondary winding value with the measurement data (Transformator Turn Ratio Test). The comparison results obtained measurements on the transformer 50 kVA tap 1 ratio of the belitannya ratio is 90.908, tap 2 is 88,802 and tap 3 is 86,605. Meanwhile, if using the formula YZN5 transformer 50 kVA comparison of the turns on tap 1 is 90.932, tap 2 is 88.767 and at tap 3 is 86.602.