Combined methods involves a combination of NDT methods for predicting the on-site strength of concrete. The combination of Ultrasonic Pulse Velocity and Rebound hammer has been studied by several researcher. The combined methods often deliver more comprehensive results. The improvement of the accuracy of the strength prediction according is achieved by the use of correction factors taking into account the influence of cement type, cement content, petrologic aggregate type, fine aggregate fraction, and aggregate maximum size. The accuracy of the combination of rebound hammer and ultrasonic pulse velocity results in improved accuracy in estimating the compressive strength of concrete.