Dehumidifier size in pints per day comes from how damp the space is: ENERGY STAR gives 20 to 30 pints for a slightly to moderately damp room under 2,000 sq ft, 25 to 40 for very damp and 30 to 50 for wet, so a 1,000 sq ft very damp basement needs about 30 pints, or 35 below grade. Enter your space above to get a single number to shop for.
How the dehumidifier size calculator works
ENERGY STAR sizes dehumidifiers by how wet the space is, not by an exact area, and gives a range for rooms under 2,000 sq ft and a minimum above that.
| How damp | Relative humidity | Under 2,000 sq ft | Over 2,000 sq ft |
|---|---|---|---|
| Slightly to moderately damp | 50 to 75% | 20 to 30 pints/day | 30 or more |
| Very damp | 75 to 90% | 25 to 40 pints/day | 40 or more |
| Wet | 90 to 100% | 30 to 50 pints/day | 50 or more |
To turn a range into one number, the calculator moves from the low end of the range at 500 sq ft to the high end at 2,000 sq ft. That placement is ours, not ENERGY STAR's. It then scales for ceilings above 8 ft and adds pints for the conditions that put more water in the air.
Pints per day = range value for the area × (ceiling ÷ 8 ft) + 5 below grade + 5 for three or more people + 5 for laundry
The three additions come from HVACBase's sizing guide (a non-government source): 5 pints for a below-grade space, 5 for three or more occupants and 5 for a washer or dryer nearby. The ceiling factor is the volume rule: a 10 ft ceiling multiplies by 1.25.
Worked examples
- Basement, 1,000 sq ft, very damp, below grade: range 25 to 40, one third of the way up is 30 pints, plus 5 for below grade is 35 pints per day.
- Crawl space, 800 sq ft, wet, below grade: 30 + 20 × 0.2 = 34, plus 5 is 39 pints per day.
- Living area, 500 sq ft, damp: 20 pints per day.
- Laundry room, 150 sq ft, damp, dryer in the room: 20 + 5 is 25 pints per day.
- Over 2,000 sq ft, very damp: ENERGY STAR gives only "40 or more", so the calculator returns 40 as a floor.
Dehumidifier size for a basement, crawl space or bedroom
The space chips fill area, dampness and the below-grade toggle. Basements and crawl spaces are the cases where undersizing hurts: an undersized unit runs nonstop, wears out early and costs more to run than a right-sized one, and ENERGY STAR notes "it's better to oversize than undersize". Bedrooms are small and land at the low end of the range.
Pints per day: old ratings against new
The test the ratings come from changed. Since June 2019 the Department of Energy runs portable dehumidifiers at 65 °F instead of 80 °F, which removes less water, so the same machine has a lower rating. ENERGY STAR's conversion for portables: an old 30 pint unit is about 20 pints now, 50 is about 30, 60 is about 35 and 90 is about 55. For whole-home units, 80 is about 70, 140 about 115 and 160 about 135. ENERGY STAR also lists updated standards from October 1, 2025. Read the label on the unit, and compare it with this page's number, which is a current rating.
Beyond the size
A dehumidifier only treats symptoms of moisture that gets in. Fix gutters and grading, seal bare crawl space soil with a vapor barrier and keep dryer vents outdoors. A bathroom fan sized in the bathroom fan CFM calculator clears showers before they reach the walls, the CFM calculator sizes airflow for a whole room, and the AC size calculator matters because an oversized air conditioner also leaves a house clammy. Work out the space with the cubic feet calculator and see the wider set in the heating and plumbing calculators hub.
The dehumidifier size chart below maps area and dampness to pints per day, so you can check the result against a box label.