What unit is used to measure humidity?

The actual humidity in terms of the water content of air is typically expressed as grams per kilogram or kilogram per kilogram. Humidity is typically expressed as a percentage of how humid it could physically be at a given temperature.

Absolute humidity is the mass of water vapor in the air divided by the mass of dry air. Relative humidity is a more common method of expressing humidity, and it is the current absolute humidity divided by the maximum possible absolute humidity at the current temperature, expressed as a percentage. A relative humidity of 45 percent is the point at which humans tend to be most comfortable.