About this tool
The Dehumidifier Size Calculator is a free, in-browser tool that recommends the moisture-removal capacity, in pints per day, that a space needs based on its floor area and how damp it is. It follows the AHAM/DOE sizing approach: pints per day equals the room area in square feet times a per-square-foot rate that rises with dampness — about 0.020 for a moderately damp room (musty smell, 50–60% relative humidity), 0.024 for very damp (visible damp spots, 60–70%), 0.028 for wet (walls sweat, 70–85%), and 0.033 for extremely wet spaces with standing water or heavy laundry.
All of the sizing math runs locally in your browser and nothing you enter is stored. Because basements and rooms containing a washer and dryer run persistently more humid than the same-size room elsewhere, toggling the basement/laundry option bumps the dampness up one level, matching common field practice. A minimum floor of 20 pints per day is applied to any conditioned space, since very small dehumidifiers rarely keep up in practice.
The result is reported both as raw pints per day and as the nearest standard unit class — 20, 30, 35, 50, or 70 pints — using modern DOE integrated-energy-factor ratings, which measure smaller numbers than the pre-2019 labels for the same real capacity. Use it as a guide: a 500-sq-ft moderately damp room lands near a 20-pint unit, while a 1,000-sq-ft wet basement points toward a 30-pint or larger class. Sealing leaks and improving drainage will always let a smaller unit do the job.