How to Calculate Dehumidifier Size Requirements

Dehumidifiers remove moisture from the air and can convert a once musty, damp place into a livable and usable space or a suitable area for storage.

Calculate the tank size of the dehumidifier you need based on the size and dampness of your space. Tank size requirements assume you will empty your tank once per day when in use.

Measure the approximate square footage of the space you want to place your dehumidifier. Area is measured by multiplying length by width.

Evaluate the dampness of your room. According to Energy Star, if your space is damp and musty only on humid days, it is considered "moderately damp." If your room is damp and musty all the time and you have damp spots on your walls and ceilings, it is considered "very damp." If your space is musty and damp and the walls and floor sweat moisture, it is considered "wet." If your floors and walls are wet and nothing is ever dry, it's considered "extremely wet."

Select a humidifier that has a capacity to hold 10 pints of water for a 500 square feet moderately damp space and add 4 pints for every additional 500 square feet. For a very damp space, select one that holds 12 pints (for a 500 square feet) and increase by 5 pints for every 500 square feet. For a 500 square foot wet space, choose one that holds 14 pints and add 6 pints for every 500 square feet. For an extremely wet space of the same size, select a dehumidifier that hold 16 pints of water and increase by 7 pints for every 500 square feet.


  • Use the chart or calculator provided by Energy Star to guide you in your selection.

About the Author

Melissa Lewis is a former elementary classroom teacher and media specialist. She has also written for various online publications. Lewis holds a Bachelor of Arts in psychology from the University of Maryland Baltimore County.