Dehumidifier Size Calculator
Pint capacity by room size and how damp the space is.
You need
30 pints/day
Post-2019 DOE rating. Older labels read about 40% higher for the same machine.
- Space area
- 600 sq ft
Estimates only. Verify quantities before ordering.
How this is calculated
Capacity in pints per day = area / 500 sq ft x a dampness factor (20 for musty or humid air, 25 for visibly damp walls or floors, 30 for wet spots or seepage), rounded up to the next standard size. Based on post-2019 DOE-rated capacities.
Enter the space's dimensions and how damp it gets, and this calculator recommends a capacity in pints per day under the current (post-2019) DOE test standard. That standard change matters when comparing: a unit rated 35 pints today removes about as much water as one labeled 50 pints under the old test, so ignore any sizing chart that predates it.
Dampness level matters as much as area. A basement that merely smells musty in summer needs far less capacity than one with visible condensation or seepage after rain. When in doubt, round up one size: a larger dehumidifier cycles less to hold the same humidity, and most units shut off at their target rather than over-drying.
Dehumidifier sizes for common spaces
Rows use post-2019 DOE pint ratings at the stated dampness.
| Space | Pints/day | Area |
|---|---|---|
| 15 x 20 ft room, musty | 15 pints/day | 300 sq ft |
| 30 x 20 ft basement, musty | 25 pints/day | 600 sq ft |
| 30 x 20 ft basement, damp | 30 pints/day | 600 sq ft |
| 40 x 25 ft basement, damp | 50 pints/day | 1,000 sq ft |
| 40 x 30 ft basement, wet | 75 pints/day | 1,200 sq ft |
Common questions
What size dehumidifier for a basement?
A typical 600 to 1,000 square foot basement that is moderately damp wants a 30 to 50 pint unit under today's ratings. Whole-basement coverage from a single portable unit works best with an open layout; closed-off rooms may need the unit moved or a second small one.
Why do dehumidifier sizes seem smaller than they used to be?
The DOE changed the test conditions in 2019 to cooler, more realistic temperatures, and measured capacities dropped about 30 to 40% on the same hardware. A modern 35 pint unit roughly equals an old 50 pint unit. Compare only within the same rating era.
What humidity should I aim for?
30 to 50% relative humidity is the comfort and mold-prevention range; 50% is the common setpoint for basements. Below 30% the air gets uncomfortably dry, and above 60% mold and dust mites thrive. A cheap hygrometer tells you where you stand before and after.
Does a dehumidifier need a drain?
Not necessarily: units collect into a bucket you empty, typically once or twice a day in damp spaces. But any unit running constantly (a basement in summer) is far more practical with its hose port draining to a floor drain or a condensate pump, and continuous-drain setup takes five minutes.