One of the measures of sustainable human development is health. Sports, such as calisthenics training, promote a healthy lifestyle. In this type of training, push-up becomes the basic exercise to maintain physical strength. Despite this exercise has been regularly performed, the way to perform a correct push-up motion is rarely discussed. This study proposed an automatic push-up counter, namely PERKASA, that practically supports the correct posture in calisthenics training. It used a simple Arduino microcontroller and two ultrasonic sensors as the main component. The counting algorithm is triggered if the body is horizontally leveled. The practical test of PERKASA has shown that the device could detect up to 92% of the correct posture for push-ups. The results indicate that the tool has functioned properly to detect deficiencies in correct posture when doing push-ups.