Structural health monitoring (SHM) system is carried out to ensure that a bridge structure remains in service condition. The bridge deflection measurement method using rotation data from a tiltmeter is considered quite promising. This study aims to obtain a mathematical model of the relationship between deflection that occurs in the middle of the span and the rotation on the bridge. The results of the analysis show that the greater the quantity of rotation value data, the regression equation has a higher level of accuracy approaching accuracy with the category of very good (≥ 90%). The percentage level of accuracy increased when the addition of a rotation sensor is added to the top chord.