Daily step count is a useful measure of physical activity. Various commercial step counting devices like activity trackers, mobile apps are available. These devices can be used in self-monitoring physical activity. Healthcare providers can use the activity trackers for monitoring patients' physical activity and also design rehabilitation programs. The objective of this study is to assess the step accuracy and usability of four commercially available activity trackers. The activity trackers selected are the Honor Band 3, the Fitbit Alta, the MI Band, and a Chinese smartwatch. The Honor band 3 is the best among wrist-worn activity trackers, with the highest accuracy and the best usability. Among the mobile-based apps, the Google fit app is the best; its step accuracy is comparable to the Honor Band 3. The variables gender and body mass index (BMI) have no effect on step accuracy. However, some devices showed significant variance in step accuracy for sloping terrain. Activity trackers assume normal gaits. In some devices , the default stride length can be corrected, which resulted in improved step accuracy, especially in the Fitbit Alta. For shorter durations ( 5 minutes), the study shows a significant difference in steps recorded among devices. However, for longer durations, there is no difference in steps recorded among devices. Except for the Chinese Smartwatch and the Pedometer App, all other devices recorded high step accuracy and usability.