This study explores the use of non-destructive ultrasonic through-transmission methods to determine rock damage levels and crack initiation stress thresholds. The research focuses on four rock types—marble, sandstone, granite, and basalt—and investigates changes in ultrasonic signal characteristics during uniaxial compression loading. Key parameters analyzed include wave velocity, amplitude, dominant frequency, and root-mean-square voltage (VRMS). The results show that the rate of signal variation can reliably estimate crack closure and initiation stress levels across the tested rocks before failure. The study compares the proposed ultrasonic methods with conventional stress-strain techniques, finding that all ultrasonic methods produce consistent estimations of crack closure and initiation stress thresholds with smaller variations between specimens. Additionally, ultrasonic methods provide earlier indications of crack initiation stress thresholds compared to conventional methods. The findings suggest that ultrasonic parameters can serve as a reliable alternative to conventional stress-strain methods for characterizing crack damage stress thresholds in rock mechanics. Future research directions include monitoring crack damage stress thresholds, implementing automated procedures, and exploring the effects of temperature, moisture, and loading conditions.This study explores the use of non-destructive ultrasonic through-transmission methods to determine rock damage levels and crack initiation stress thresholds. The research focuses on four rock types—marble, sandstone, granite, and basalt—and investigates changes in ultrasonic signal characteristics during uniaxial compression loading. Key parameters analyzed include wave velocity, amplitude, dominant frequency, and root-mean-square voltage (VRMS). The results show that the rate of signal variation can reliably estimate crack closure and initiation stress levels across the tested rocks before failure. The study compares the proposed ultrasonic methods with conventional stress-strain techniques, finding that all ultrasonic methods produce consistent estimations of crack closure and initiation stress thresholds with smaller variations between specimens. Additionally, ultrasonic methods provide earlier indications of crack initiation stress thresholds compared to conventional methods. The findings suggest that ultrasonic parameters can serve as a reliable alternative to conventional stress-strain methods for characterizing crack damage stress thresholds in rock mechanics. Future research directions include monitoring crack damage stress thresholds, implementing automated procedures, and exploring the effects of temperature, moisture, and loading conditions.