Relative humidity is the ratio of the actual water vapour content of the air to the maximum amount of water vapour the air can hold at a given temperature. It is expressed as a percentage and ranges from 0% (completely dry air) to 100% (completely saturated air).
Specific humidity is the mass of water vapour per unit mass of dry air. It is expressed in grams of water vapour per kilogram of dry air (g/kg). Specific humidity provides information about the actual water content in the air, regardless of temperature.
Absolute humidity is the mass of water vapour per unit volume of air. It is expressed in grams of water vapour per cubic meter of air (g/m³). Absolute humidity depends on both temperature and the amount of water vapour present in the air.
The amount of water held in air can vary greatly depending on the location, time of day, season, and weather conditions. Warm air can hold more water vapour than cold air, and the air near large bodies of water tends to be more humid.
