Abstract: The experimental method of measuring concrete damage scale was studied based on the digital image correlation (DIC) technique. Three-point bending fracture tests were performed and the damage scales during the crack propagation processes were obtained. The effects of the specimen size and maximum aggregate size on the permissible damage scale were studied. A theoretical method was used to calculate the permissible damage scale. The experimental results indicate that the comparisons of the load-crack mouth opening displacement curves obtained by the DIC method and by the clip gauges show a good agreement. The permissible damage scale values obtained from the theoretical method agree well with the experimental results. Therefore, it verifies the reliability of the proposed experimental method of measuring the damage scale. The permissible damage scale increases with the specimen size but with a slow growth rate and decreases with the maximum aggregate size.