Homeowners can determine the exact humidity level and amount of excess humidity in their homes through a hygrometer. If you don't have one available, you can estimate it by how the humidity feels in your home.
Slightly heavy air: 50%-60%
Occasional musty smell: 60% to 70%
Wet spots around the home: 70% to 80%
Seepage on walls or the presence of mold: 80% to 100%