The total surface area of an adult is about 2 m, and the mid- and far-infrared emissivity of skin and most clothing is near unity, as it is for most nonmetallic surfaces. Skin temperature is about 33 °C, but clothing reduces the surface temperature to about 28 °C when the ambient temperature is 20 °C. Hence, the net radiative heat loss is about P net = P emit − − P absorb = 100 W . The total energy radiated in one day is about 8 MJ, or 2000 kcal (food calories). Basal metabolic rate for a 40-year-old male is about 35 kcal/(m ·h), which is equivalent to 1700 kcal per day, assuming the same 2 m area. However, the mean metabolic rate of sedentary adults is about 50% to 70% greater than their basal rate.