Free tool
Dehumidifier Size Calculator
Square footage in, pints-per-day out — on the modern AHAM 2019 test standard, with the two traps that make people buy the wrong unit: old inflated labels and cold-basement icing.
How the sizing works
The chart behind this tool is the industry sizing table used since the 2019 AHAM test change, anchored at 300 / 500 / 800 / 1,200 sq ft for four dampness levels and interpolated between them. Two adjustments matter in real homes: add ~25% capacity for high ceilings or spaces open to adjacent rooms, and in a cool basement pick a low-temperature-rated unit regardless of size. Hold the space at 45–55% relative humidity — below 60% is where mold growth stops being fed.
Picking a unit? Our tested picks: best dehumidifiers for water damage. Damp that never improves has a cause — start with why is my basement always wet.