Dehumidifier Size Calculator
Determine the correct dehumidifier capacity in pints per day for any room size and humidity level.
Covers basements, bedrooms, and crawl spaces.
Dehumidifier sizing is measured in pints of moisture removed per 24 hours. Choosing the wrong size means your unit either runs constantly and fails early (undersized) or short-cycles and never properly dries the air (oversized).
The core sizing formula:
Pints/Day = Room Volume (cu ft) × Moisture Factor / 1,000
- Room Volume = Length × Width × Height (in feet)
- Moisture Factor depends on how damp the space is:
- Moderately damp (musty smell): 0.8
- Very damp (visible moisture on walls): 1.2
- Wet (standing water present): 1.6
- Extremely wet (flooding history): 2.0
Worked example: Basement = 30 ft × 20 ft × 8 ft = 4,800 cu ft Condition: Very damp (factor = 1.2) Required capacity = 4,800 × 1.2 / 1,000 = 5.76 pints/day → round up to 30-pint unit
Adjustment factors:
- High humidity climate: add 10%
- Space used as laundry room: add 5–10 pints/day
- Multiple occupants sleeping in space: add 2–3 pints/person/night
Standard capacities available: 20, 30, 50, 70, and 90-pint units. For most residential basements under 1,000 sq ft, a 30-pint unit suffices in mild climates. In southeastern US or coastal regions, step up one size.
Practical tips:
- Run in continuous drain mode when possible — emptying the bucket manually is often forgotten
- Optimal target humidity is 45–55% RH for comfort and mold prevention
- Below 60°F, most compressor dehumidifiers lose efficiency — choose a unit rated for low temperatures if your basement gets cold
- Energy Star-rated units use roughly 15% less electricity than standard models