Frost Point Calculator

About this calculator

Frost point is the ice-surface counterpart of dew point: it's the temperature to which air must be cooled, at constant pressure and moisture content, for water vapor to become saturated with respect to ice and begin depositing as frost rather than condensing as liquid dew. Because the saturation vapor pressure over ice is slightly lower than over supercooled liquid water at the same sub-zero temperature, the frost point is always a bit higher than the dew point would be if water stayed liquid at that temperature.

Meteorologists use frost point below freezing instead of dew point for accuracy, while refrigeration and cold-storage engineers, aviation professionals (assessing airframe or runway icing risk), and natural-gas pipeline operators (controlling water-dew-point specifications to prevent hydrate formation) rely on it as a practical threshold for when frost or ice will start forming on a surface.