The amount of moisture in the air is known as relative humidity (RH) and is always measured in percentage. The normal RH levels should be between 30-40%. Anything above these levels risks growth of bacteria and other ills associated with high humidity. Some dehumidifiers come with a built-in humidistat—which is simply a device that allows you to set the RH level that you require for the room. A dehumidifier with this unit will cycle on and off and maintain the set RH without requiring you to keep changing it. If your dehumidifier doesn’t have a built-in humidistat, you can still keep the RH in check by using a hygrometer to measure the RH. Place the hygrometer close to the dehumidifier while it’s working and it will show the exact RH at the time. You can then adjust the settings accordingly. (Read more in our dehumidifier buying guide here)