风寒指数是一种暴露于皮肤的表观气温，是由气温与风速所对应的函数。

风寒指数是根据风寒效应所定立的指数。而风寒效应的出现是由于风也会影响我们对冷的感觉，引致温度计的读数有些时候可与人们对冷暖的感觉有明显的分别。在冬季期间，持续的强风天气会令我们对冷的感觉来得更强烈。这个风速与人体对外界温度感觉的关系，称为「风寒效应」。

Wind-chill or windchill, (popularly wind chill factor) is the perceived decrease in air temperature felt by the body on exposed skin due to the flow of air.

Wind chill numbers are always lower than the air temperature for values where the formula is valid. When the apparent temperature is higher than the air temperature, the heat index is used instead.