Thinking. Most people don't realize how much energy the brain uses. According to The Physics Factbook the human brain accounts for less than 2% of a person's total weight but the brain consumes roughly 20% of the body's total energy. Since the average power consumption of a typical human adult body is around 100 watts that means the brain consumes around 20 watts of power. In comparison the human heart only uses around two watts of power to beat and pump blood through the body.