Determination of antioxidant/capacity in the dietary, food, drugs, and biological samples is an interesting approach for testing the safety of these compounds and for drug development. Investigating the google searching engines for the words (measurement + antioxidant + capacity) yielded more than 20 million results, which makes it very difficult to follow. Therefore, collecting the common methods to measure the antioxidant activity/capacity in the food products and biological samples will reduce the burden for both the students and researchers. Nowadays, it is widely accepted that a plant-based diet with a high intake of dietary sources such as vegetables, fruits, and other nutrient-rich plant foods may decrease the effect of oxidative stress-related diseases. In this review article, we have provided the most recent advances in the most common methods used for evaluating the antioxidant potential of numerous food products, plant extracts, and biological fluids. We have also provided detailed procedures on how to perform them and analyze the results. This review article shall be a comprehensive reference for all techniques used in this area.