美国国家气象中心根据Steadman（1979）的研究，依据温度、相对湿度等相关气象因子，导出热指数公式：
HI = -42.40+ (2.04901523 * [TEMP])+ (10.14333127 * [HUMIDITY])-(.22475541 * [TEMP] * [HUMIDITY])-(.00683783 * ( [TEMP]^2 ))-(.05481717 * ( [HUMIDITY]^2 ))+(.00122874 * ( [TEMP] ^2) *[HUMIDITY]) +(.00085282 * [TEMP] * ( [HUMIDITY]^2 ))-(.00000199* ( [TEMP] ^2 ) * ( [HUMIDITY] ^2))