What measurement indicates the amount of water vapor present in a given amount of air?

The measurement that specifically indicates the amount of water vapor present in a given amount of air is known as the humidity ratio. This term represents the mass of water vapor per unit mass of dry air and is typically expressed in grains of moisture per pound of dry air or in grams per kilogram of dry air. This ratio provides a direct quantification of the moisture content in the air, making it essential for various applications in drying processes and environmental controls.

Relative humidity is the percentage of moisture in the air compared to the maximum amount of moisture the air can hold at a given temperature, while absolute humidity measures the total mass of water vapor in a given volume of air, regardless of temperature or pressure. Dew point is the temperature at which the air becomes saturated with moisture and condensation begins; while it is related to humidity, it does not provide the direct measurement of water vapor content like the humidity ratio does.