The relative humidity is a measure of the amount of water vapor in the air (at a specific temperature) compared to the maximum amount of water vapor air could hold at that temperature, and is given as a percentage value. Relative humidity depends on the temperature of the air, as warm air can hold more moisture than cold air. A relative humidity of 100 percent indicates that the air is holding all the water it can at the current temperature, and any additional moisture at that point will result in condensation. A relative humidity of 50 percent means the air is holding half the amount of moisture that it could. As the temperature decreases, the amount of moisture int he air doesn't change, but the relative humidity goes up (since the maximum amount of moisture that cooler air can hold is smaller).
When referring to pet care, the terms humidity and relative humidiy are usually used interchangably. For an example, if we say the appropriate humidity for hermit crabs is 70-80 percent, we are speaking of the relative humidity.
To determine the relative humidity in the air, for example in a terrarium, you need to use a device called a hygrometer.
Also Known As: RH
White's tree frogs should have a humidity of 50-60 percent.