Dehumidifier Size Calculator
Find what size dehumidifier you need in pints per day from the room size and how damp it is, using the Energy Star sizing guidance and the 2019 DOE test ratings.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Dehumidifier capacity
- 20 pints per day
- Energy Star sizing guidance for a moderately damp space
- Recommended retail size
- 20 pint unit
- Smallest common size that meets the load
- Floor area
- 500 sq ft
- 8 ft ceiling
- Equivalent pre-2019 rating
- about 28 pints per day
- Units tested under the old 80 F method carried numbers about 40% higher; a 70 pint unit from before 2019 is about 50 pints today
Dehumidifier Size formula
Area = Length x Width x (Ceiling height / 8, when the ceiling is above 8 ft)
Pints per day = Energy Star guidance value for that area and dampness level (see table), interpolated between rows
Add 5 pints for many occupants, laundry or a shower in the space
Liters per day = Pints per day x 0.473Worked example
A 30 x 40 ft basement (1,200 sq ft) with damp spots on the walls (very damp) that also holds the laundry. The very damp column reads 25 pints at 1,000 sq ft and 30 pints at 1,500 sq ft, so 1,200 sq ft is 25 + (200 / 500) x 5 = 27 pints. Add 5 pints for the laundry: 32 pints per day.
The next retail size up is a 35 pint unit, which removes about 16.6 liters a day. Under the old test method that same machine would have been labeled roughly 32 x 1.4 = 45 pints.
Quick reference
| Floor area | Moderately damp | Very damp | Wet | Extremely wet |
|---|---|---|---|---|
| 500 sq ft | 20 pints | 20 pints | 25 pints | 30 pints |
| 1,000 sq ft | 22 pints | 25 pints | 30 pints | 35 pints |
| 1,500 sq ft | 25 pints | 30 pints | 35 pints | 40 pints |
| 2,000 sq ft | 30 pints | 35 pints | 40 pints | 45 pints |
| 2,500 sq ft | 35 pints | 40 pints | 45 pints | 50 pints |
| 3,000 sq ft | 40 pints | 45 pints | 50 pints | 55 pints |
How to pick the right capacity
Dehumidifiers are rated by how many pints of water they can pull from the air in 24 hours at 65 F and 60% relative humidity. Energy Star guidance pairs floor area with four dampness levels: a space that only smells musty in humid weather needs the least, a space with standing water the most. Measure the floor, pick the honest dampness level, and add 5 pints when a laundry, shower or a crowd of people adds moisture.
When the result lands between sizes, go up. A unit at its limit runs nonstop and never reaches the set point; one size up pulls the space to 50% and cycles off, which costs less to run over a summer. Retail sizes are 20, 22, 30, 35, 40 and 50 pints, and the 50 pint class is where built-in condensate pumps show up, typically $50 to $80 more. Anything bigger is a whole-house unit ducted into the return, typically $1,500 to $3,000 installed.
Old ratings, placement and drainage
Any chart or review written before mid-2019 uses the old 80 F test, under which the same machines scored about 40% higher. A neighbor's 70 pint unit is what a 50 pint unit is today, and a 50 pint model from that era corresponds to roughly 35 pints now. Compare only ratings measured the same way.
Set the unit in the open near the middle of the basement with 12 in clear around the grilles, not in a closet or a utility corner. The bucket holds 1.5 to 2 gallons and shuts the unit off when full, so a 30 pint load fills it twice a day. Thread a garden hose onto the drain port and run it downhill to a floor drain, sump pit or utility sink. Where no drain sits lower than the unit, a pump model lifts condensate about 15 ft. Leave the thermostat fan on Auto: in cooling season the On setting blows the condensate off the coil back into the house.
Fix the water first where you can. IRC R401.3 wants grade falling 6 in over the first 10 ft from the foundation; extend downspouts 4 to 6 ft, patch cracks and vent the dryer outdoors. A dehumidifier treats the symptom, not the leak. Standing water is a sump pump job first, and a basement that stays below 41 F needs a unit with auto defrost or a desiccant model.
What this calculator leaves out
The result is a capacity. Not included: the drain hose or condensate pump, a 15 A receptacle within cord reach (extension cords void most warranties), the running cost of 500 to 700 W at full output, and monthly filter cleaning. Not included either: the grading, downspout, sump pump and crack repair that lower the dampness level, or a whole-house unit and its ducting when the load passes 50 pints.
Mistakes that cost money
- The bucket fills in 4 to 6 hours at full output and the unit shuts off until emptied; run the hose to a floor drain.
- The drain hose is gravity fed and must run downhill the whole way; a kink or uphill run backs up and shuts the unit off.
- Pushed against a wall, the unit recirculates its own dry exhaust and short cycles; leave 12 in clear on the intake and exhaust sides.
- Running the HVAC fan in On instead of Auto during cooling season re-evaporates water off the coil and raises indoor humidity 5 to 10 points.
- Running a dehumidifier with basement windows open in summer pulls in humid outdoor air faster than it dries; keep windows closed and the door shut.
- Set the humidistat at 50 percent, not 35; a 50 pint unit draws 500 to 700 W and never shuts off at 35.
Key facts
- In 2019 the DOE changed the dehumidifier test conditions from 80 F to 65 F at 60% relative humidity, so a unit once labeled 70 pints is now rated about 50 pints; the machines did not change, the test did.
- One pint is 0.473 liters, so a 50 pint dehumidifier removes about 23.7 liters, or 6.25 gallons, of water a day at the rated conditions.
- The EPA recommends keeping indoor relative humidity between 30 and 50%; mold and dust mites thrive above 60%.
- Standard compressor dehumidifiers frost up below about 41 F; a cold basement needs a unit with auto defrost or a desiccant model.
- This calculator assumes an 8 ft ceiling; a 10 ft ceiling holds 25% more air, so the area is scaled up by the same amount.
Frequently asked questions
What size dehumidifier for a 1,000 sq ft basement?
A moderately damp 1,000 sq ft basement needs about 22 pints per day, a very damp one 25 pints, a wet one 30 and one with standing water 35. Buy the next retail size up, so a 22, 30, 30 or 35 pint unit respectively.
Why is my 70 pint dehumidifier now called 50 pints?
The DOE test changed in 2019 from 80 F to 65 F, which is closer to a real basement. The cooler air holds less water, so the same machine removes fewer pints in the test. Old 70 pint units are roughly 50 pint units under the new label.
Is a bigger dehumidifier better?
Up to a point. A unit sized one step above the chart reaches the set point faster and runs less often, which is more efficient than a small unit running nonstop. Going far bigger costs more up front and uses more power each cycle without drying the space any better.
Do I need a dehumidifier with a built-in pump?
Only when nothing lower than the unit can take the water. The standard drain port is gravity only and needs a floor drain, sump pit or utility sink below it with the hose running downhill the whole way. A pump model lifts the condensate about 15 ft to a laundry sink or out a basement window and typically costs $50 to $80 more than the same capacity without one.
Sources and references
- Dehumidifiers: capacity sizing table by room size and dampness (ENERGY STAR)
- Dehumidifier Testing and Capacity: the 2019 DOE test procedure change from 80 F to 65 F (ENERGY STAR)
- 10 CFR Part 430, Subpart B, Appendix X1: Uniform Test Method for Measuring the Energy Consumption of Dehumidifiers (U.S. Department of Energy, eCFR)
- A Brief Guide to Mold, Moisture and Your Home (indoor humidity 30 to 50%) (EPA)
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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.