In normal conditions of temperature and atmosphere, the rate of cooling of dead body is:

The dead body cools at an average rate of 1.5 degree F per hour in temperate climate and 0.75 degree F in a tropical climate. According to Simpson, the cooling of the body is the only reliable indicator of the lapse of time during the first 18 hours after death. Factors controlling the cooling rate are: Condition of the body Clothing Atmospheric temperature Mode of death Medium Ref: Forensic Medicine By P.V. Guhara page 62.