Relative Humidity

A type of humidity that considers the ratio of the actual vapor pressure of the air to the saturation vapor pressure. It is usually expressed in percentage.

Ratio that compares the amount of water vapor in the air to the saturation amount. The ratio of the mixing ratio of the ambient air and the saturation mixing ratio of the same air with the same pressure and temperature. Relative humidity is usually expressed as a percentage. When using relative humidity as an indication of absolute moisture quantity, caution must be used, because colder air has a smaller saturation mixing ratio than warmer air.

A dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself does not directly indicate the actual amount of atmospheric moisture present. See dew point .