Dehumidifier Size Calculator
Estimate the pints-per-day capacity your dehumidifier needs from the room’s square footage and how damp it feels, then match it to a standard unit size.
How it works
Load = 10 + (area − 500) ÷ 500 × 4 + dampness allowance · Size = smallest standard unit ≥ load
Dehumidifier capacity is rated in pints of water removed per day. Sizing scales with floor area and, more sharply, with how wet the space actually is: a musty basement needs far less than one with visible seepage. This tool starts from the common baseline of about 10 pints per day for a 500 ft² moderately damp room, adds capacity for larger areas, then adds a fixed allowance for wetter conditions before rounding up to a standard unit (10, 20, 30, 35 or 50 pints under the current DOE test method).
Worked example
A 1,000 ft² basement that feels very damp: the area term is 10 + (1,000 − 500) ÷ 500 × 4 = 14 pints, plus 4 pints for “very damp” = 18 pints/day. The smallest standard unit that covers 18 is a 20-pint dehumidifier.
Frequently asked questions
Is a bigger dehumidifier always better?
A slightly larger unit reaches the target humidity faster and runs less often, which can save energy. But an oversized unit in a small room short-cycles, and paying for capacity you never use wastes money up front. Match the size to the load.
Why do modern pint ratings look smaller than old ones?
The DOE changed its test conditions in 2019 to a cooler, more realistic 65°F. A unit once labelled “70 pint” is now rated around 50 pints for the same hardware, so compare like-for-like against today’s ratings.
Does a colder basement need a different unit?
Yes. Standard compressor dehumidifiers lose capacity and can frost up below about 65°F. For cold cellars or garages, look for a low-temperature model or a desiccant dehumidifier that works down to near freezing.
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This calculator is for educational purposes. Double-check important results before acting on them.