Frost or freezing occurs when the temperature of air falls below the freezing point of water (0 °C, 32 °F, 273.15 K). This is usually measured at the height of 1.2 m above the ground surface. Frost or freezing occurs when the temperature of air falls below the freezing point of water (0 °C, 32 °F, 273.15 K). This is usually measured at the height of 1.2 m above the ground surface.