The electromechanical properties of La3Ga5SiO14 (LGS) and La3Ga5.5Ta0.5O14 (LGT) have been studied at room temperature on 25 samples using resonant ultrasound spectroscopy (RUS). The RUS method facilitates simultaneous determination of all independent elastic and piezoelectric constants of a sample within the same frequency range and yields sample parameters with high internal consistency. Consequently, the spread of the experimental results presented here is significantly lower than the scatter of literature data obtained by different experimental techniques.