Dehumidifier Size Calculator
Find the dehumidifier capacity, in pints per day, that a room or basement needs.
Your space
ENERGY STAR describes "Very Damp" as: space consistently feels and smells damp. Damp spots appear on walls and floors.
Results
For a very damp space of 180 sq ft, ENERGY STAR's chart recommends 25–40 pints per day.
Recommended capacity
25–40 pints per day
ENERGY STAR's chart puts a very damp space under 2,000 sq ft at 25 to 40 pints per day.
ENERGY STAR calls these minimum capacities and says it's better to oversize than undersize: choose a model rated at 25 pints per day or more on its current label, and if you are between two, take the larger.
| Condition without dehumidification | Small-medium room (under 2,000 sq ft) | Large room (over 2,000 sq ft) |
|---|---|---|
| Slightly to Moderately Damp (50–75% RH) | 20–30 | 30+ |
| Very Damp (75–90% RH) | 25–40 | 40+ |
| Wet (90–100% RH) | 30–50 | 50+ |
Floor area (chart unit): 180 sq ft
Chart column: Small-medium room (under 2,000 sq ft)
Compare this with the capacity on a current label. If the space usually sits below 65°F, look for a model specified for lower temperatures.
How this works
What size dehumidifier you need depends on the floor area and how damp the space is. ENERGY STAR's chart puts any space under 2,000 sq ft, such as a 1,000 sq ft basement, at 20–30 pints per day if it is slightly to moderately damp (50–75% relative humidity), 25–40 pints per day if it is very damp (75–90% relative humidity), and 30–50 pints per day if it is wet (90–100% relative humidity). Over 2,000 sq ft it gives only minimums: 30+, 40+ and 50+ pints per day.
The calculator turns your length × width, or the area you enter, into square feet, the unit the chart uses, and picks the column: small-medium below 2,000 sq ft, large at 2,000 sq ft or more. The condition you choose picks the row, and the cell where they meet is the result. Within a column the chart gives one range for every area, so a 200 sq ft room and a 1,900 sq ft one get the same range; the calculator does not invent a finer split. ENERGY STAR calls these minimum capacities and says it's better to oversize than undersize. Metric entries are converted with the exact foot definition, and the area is rounded only for display.
Old and new pint ratings
The pints on a dehumidifier label changed in June 2019. DOE's test procedure (10 CFR 430, Subpart B, Appendix X1) now rates a portable dehumidifier at 65°F and 60% relative humidity, where the old test used 80°F. There is less water to remove in cooler air, so the same machine collects less in the test and gets a lower rating: an old 50-pint unit is not a new 50-pint unit. ENERGY STAR publishes the chart above with a note that capacity options have changed, so compare its ranges with the capacity on a current label. ENERGY STAR's rough match between the two scales is below; it notes that the real change varies by model. No official conversion factor exists, so the calculator does not convert old ratings.
| Old rating (through 2019) | Approximate new rating (2020) |
|---|---|
| 30 | 20 |
| 40 | 25 |
| 50 | 30 |
| 55 | 30–35 |
| 60 | 35 |
| 70 | 40–45 |
| 90 | 55 |
Sources: ENERGY STAR, Dehumidifiers (sizing chart and buying guidance); ENERGY STAR, Dehumidifier Testing and Capacity (old vs new ratings); eCFR, 10 CFR Part 430 Subpart B, Appendix X1 (DOE dehumidifier test procedure), checked 2026-10-30.
Worked example: a damp bedroom
A 12 x 15 ft bedroom is 180 sq ft. It always smells damp and has damp spots on the walls, which is ENERGY STAR's "Very Damp" condition (75–90% relative humidity). 180 sq ft is under 2,000 sq ft, so it uses the small-medium room column, and the chart gives 25–40 pints per day. A current-label model rated anywhere from 25 to 40 pints fits. For scale, ENERGY STAR's old-vs-new table puts an old 50-pint unit at about 30 pints today, so an old 50-pint unit would land inside this range.
A second example: a wet basement
A finished basement of 50 x 45 ft is 2,250 sq ft. The walls sweat in summer, which is ENERGY STAR's "Wet" condition. 2,250 sq ft is over 2,000 sq ft, so it uses the large room column, where the chart gives 50+ pints per day: at least 50 pints, with no upper figure. If the basement usually sits below 65°F, choose a model specified for lower temperatures. Before buying, check the downspouts and the soil slope outside, since less water coming in means less for the unit to remove.
Common mistakes
Comparing an old pint rating with a new one
A dehumidifier labelled before the 2019 test change and one labelled today are not rated on the same scale. ENERGY STAR's table puts an old 50-pint portable at roughly 30 pints on the new rating. Buying a new 50-pint unit to replace an old 50-pint one is a size up, not a like-for-like swap.
Buying below the range to save money
ENERGY STAR presents the chart as an estimate of the minimum capacity and says it's better to oversize than undersize. A unit below the range buys less than the minimum ENERGY STAR estimates for that space and condition.
Treating the large-room figure as a target
Above 2,000 sq ft the chart gives only a minimum, written with a plus sign: 30+, 40+ or 50+ pints per day. It is a floor. For a big, very damp space, look above it rather than stopping at it.
Running it with the doors and windows open
The chart sizes the space you enter, not the outdoors or the rest of the house. ENERGY STAR says doors and windows to the space should be closed while the unit runs, so the space is dehumidified as efficiently as possible.
Buying a bigger unit instead of reducing the moisture
ENERGY STAR says reducing sources of moisture can reduce your need for dehumidification. Its list includes extending downspouts away from the foundation, keeping gutters clear, sloping soil away from the house, venting the clothes dryer outdoors and using bathroom and kitchen fans. A wet basement with water pooling at the foundation needs those fixes first.
When this estimate stops applying
- Exactly 2,000 sq ft: ENERGY STAR's columns read "under 2,000" and "over 2,000", so 2,000 itself is in neither. This calculator uses the larger column, following ENERGY STAR's advice that it's better to oversize than undersize.
- Spaces usually colder than 65°F: frost can form on the coils, so the rating may not hold. Look for a model specified for lower temperatures.
- Whole-house dehumidification through the ducts: the chart is for portable units. Whole-home dehumidifiers have their own rating and should be sized and installed by a professional.
- Standing water or active flooding: the chart's wettest row is 90–100% relative humidity with sweating walls or seepage. Water on the floor is outside the chart.
- Several connected rooms: the chart sizes one space with its doors and windows closed. If the doors between rooms stay open, measure the whole connected area, or close the space off and size it alone.
FAQ
I'm replacing an old dehumidifier. How do I pick the new one's size?
Start from how much water the old one collects: ENERGY STAR says that if you are replacing an existing dehumidifier, you can judge by how much water you empty each day. If you only know the old label, ENERGY STAR's old-vs-new table in How This Works gives a rough match, for example an old 70-pint portable at about 40–45 pints on today's rating. ENERGY STAR adds that the change varies by model and that manufacturers may give more reliable comparisons.
Will a dehumidifier work in a cold basement?
It may struggle below 65°F. ENERGY STAR says frost can form on the condensing coils if the air drops below 65 degrees, which can make the compressor cycle on and off without removing moisture, and suggests a model specified for lower temperatures if your space is usually colder than that. Some models have an anti-frost sensor that switches the unit off as the air gets too cold.
What humidity should I set the dehumidifier to?
ENERGY STAR gives 30% to 50% relative humidity as the generally optimum range for a building, and says anything above it may promote mold growth. In colder climates during the heating season, it recommends 30% to 40% to prevent window condensation. Every ENERGY STAR certified dehumidifier has a built-in humidistat, so you set the level and the unit cycles on and off to hold it.
How do I tell which dampness condition my space is in?
Measure it if you can: a hygrometer, a gauge that reads relative humidity, tells you which band you are in (50–75%, 75–90% or 90–100%). Without one, use ENERGY STAR's descriptions. Slightly to moderately damp: the space feels damp, with a musty odor that may come and go. Very damp: it always feels and smells damp, with damp spots on walls and floors. Wet: walls or floor sweat, or there is seepage.
Why doesn't the calculator ask for ceiling height?
Because ENERGY STAR's method does not use it. ENERGY STAR says the capacity you need depends on two factors: the size of the space and its conditions without dehumidification, and its chart is set by floor area. No source used here gives a ceiling-height adjustment, so this calculator does not invent one.
Is there a separate size for basements?
No. ENERGY STAR's chart has no basement column, and this calculator adds no basement factor. The rating itself already leans that way: DOE's current test rates portable dehumidifiers at 65°F, which ENERGY STAR says was chosen to reflect expected performance in a basement setting. Pick the dampness condition that matches your basement and check the temperature question above.
Does this chart size a whole-house dehumidifier?
No. ENERGY STAR presents it as the chart for portable dehumidifiers. Whole-home units connect to the home's air ducts, are rated under a different test condition (73°F in DOE's procedure), and ENERGY STAR says they should be sized and installed by a professional. It describes them as most useful in relatively well sealed homes with central air that see humidity above 55% throughout the house.
What does the pints-per-day rating actually measure?
It is the water the unit collects in 24 hours at fixed test conditions, not a promise for your room. DOE's test procedure rates a portable dehumidifier at 65°F and 60% relative humidity. In your space it will collect more or less depending on the air: ENERGY STAR notes there is less water to remove in cooler air, which is why ratings fell when the test was moved to a cooler temperature.
Where should I put the dehumidifier?
Where air can reach it, with the space closed off. ENERGY STAR says a unit without top-mounted discharge should sit away from walls and furniture so air can circulate around it, and that doors and windows to the space should be closed while it runs. Keep it away from dust sources such as woodworking tools, which can clog the coils, and plug it into a properly grounded outlet.