What is "relative humidity"

Humidity \Hu*mid"i*ty\, n. [Cf. F. humidit['e].]

1. Moisture; dampness; a moderate degree of wetness, which is perceptible to the eye or touch; -- used especially of the atmosphere, or of anything which has absorbed moisture from the atmosphere, as clothing.

2. Specifically: The content of water vapor in the air, expressed as a percent of the maximum amount of water vapor that the air can hold at the given temperature; also called relative humidity. The capacity of the air to hold moisture increases with temperature, so if the temperature changes without changing the absolute content of the atmospheric moisture, the relative humidity will also change.

   relative humidity Same as humidity[2].

   Note: In hygrometrical reports (as of the United States Signal Service) complete saturation of the air by water vapor is designated by a relative humidity of 100, and its partial saturation by smaller numbers in direct proportion to the actual content of water vapor.

n. The ratio of the actual amount of water vapor (absolute humidity) present in the air to the saturation point at the same temperature, usually expressed as a percentage.

n. the ratio of the amount of water in the air at a give temperature to the maximum amount it could hold at that temperature; expressed as a percentage

Relative humidity (abbreviated RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. Relative humidity depends on temperature and the pressure of the system of interest. It requires less water vapour to attain high relative humidity at low temperatures; more water vapour is required to attain high relative humidity in warm or hot air.