Estimate based on the older AHAM rating (80 F, 60% humidity). Newer labels use a different test and show lower numbers, so choose a larger unit when comparing.
How to use this calculator
Enter the floor area of the room or basement and choose how damp it is. Press Calculate to see how many pints of moisture a day you need to remove and the nearest standard dehumidifier size.
The formula
Capacity = base pints for 500 sq ft + extra pints for each additional 500 sq ft
Base (500 sq ft): 10, 12, 14 or 16 pints per day depending on dampness
Gallons per day = pints ÷ 8
Example: A moderately damp 1,000 sq ft basement needs about 14 pints a day. The nearest standard unit is 20 pints per day.
What your dehumidifier size result means
The calculator estimates how many pints of water per day a dehumidifier needs to remove to keep your space dry. It starts with a base amount for the first 500 square feet, set by how damp the space is, then adds capacity for each extra 500 square feet. It then shows the nearest standard size to shop for.
A worked example
A moderately damp 1,000 square foot basement needs about 14 pints a day. That is about 1.75 gallons of water each day. Since dehumidifiers come in set sizes, the nearest standard unit is 20 pints per day. A smaller, moderately damp 500 square foot room needs about 10 pints a day.
What changes the size you need
- Dampness. A space with wet spots or seepage needs far more capacity than one that only smells musty in summer.
- Climate. Humid summers mean longer run times and higher loads.
- Air leaks and activity. Laundry, showers, open doors and unsealed basement walls add moisture.
- Temperature. Most compressor dehumidifiers remove less water in cool basements. Some models are built to work better at low temperatures.
Reading the capacity label
This calculator uses the older AHAM rating, measured at 80°F and 60% humidity. Newer labels are tested at cooler conditions, so the same machine shows a lower number. A unit once sold as about 50 pints may be labeled around 35 pints today. When comparing, size up if the label uses the newer standard.
Tips and common mistakes
- Use an inexpensive hygrometer to check that the unit is reaching your target humidity.
- Set up continuous drainage with a hose to a floor drain, or buy a model with a pump, so you are not emptying the bucket every few hours.
- Clean the air filter every few weeks so airflow stays strong.
- Keep doors and windows closed while it runs.
- Do not use it as the only fix for a wet basement. Check gutters, downspouts and grading first.
Cost and planning
Larger units cost more up front but may cycle less. Look for an ENERGY STAR model, which typically uses less power for the same moisture removed. For a whole basement or a damp crawlspace, a ducted whole-house system installed by an HVAC pro may be worth comparing.
