| Relative humidity is defined as the ratio of the current amount of water vapor in the air to the maximum amount
to be contained at the current air temperature.
For example, the air at 20°C can hold, at a maximum, about 17grams of water vapor per cubic meter.
Air holding this much moisture is considered "saturated" and said to have 100% relative humidity.
If the air becomes drier up to the point where it only contains 8.5grams of moisture per cubic meter,
then the air is holding 50% of its maximum capacity. The relative humidity is then 50%.
The capacity of air to hold water vapor is heavily dependent on its temperature. The warmer the air, the more moisture it can contain.
The air can hold about 30grams of moisture per cubic meter at 30°C or about 75% more than it can at 20°C.
The air at 60°C can hold water about fifteen times that at 10°C.
Sometimes absolute humidity is used as a measure. It denotes the actual amount of water vapor in the air in gram per cubic meter.