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Young pigs 4 to 7 wk old (7~15 kg) were exposed to 20 factorial combinations of five air temperatures (20, 24, 28, 32, and 36C) and four air velocities (0.1, 0.5, 1.0, and 1.5 m/s). Infrared imaging (0.06C sensitivity) was used to simultaneously quantify postural pattern and surface temperature (T s ) of the pigs. Three postural indexes were evaluated for expressing thermal comfort level of the pigs: (1) ratio of occupied floor area (A f ) to the total surface area of the pigs index I f ; (2) ratio of A f to its maximum possible valueindex I m ; and (3) A f per 100 kg body massindex A f(100) . The pigs shared common thresholds of postural indexes I f = 0.20~0.24 and I m = 0.75~0.84 and T s of 34.5~36.3C for the thermoneutral zone (TNZ). In comparison, index A f(100) of TNZ was greatly dependent on pig age or size. The numerical indexes (I f and I m ) provide objective, quantitative assessment of thermal comfort of the pigs. Functional relationships were established between I m and T s . Moreover, I m was used to quantify the effects of air velocity on the effective environmental temperature of the pigs at cool to warm ambient temperatures.