How to judge a damp room
Measure the room's area, including any part of the basement open to it. Then find out how damp it really is. A cheap hygrometer gives you a reading after a few hours, and that is far better than a guess. ENERGY STAR's chart has three bands: 50 to 75 percent relative humidity is slightly to moderately damp, 75 to 90 is very damp, and 90 to 100 is wet.
If you have no meter, go by signs. A musty smell points to the lowest band. Damp patches on walls or floors suggest the middle one, and standing water or seepage means the top. Bear in mind that a dehumidifier deals with the moisture in the air and does nothing about the water getting in, so fix any leak or seepage first.
Check the temperature too. ENERGY STAR says that below 65 degrees you should consider a unit specified for lower temperatures, because frost can form on a standard one. Many basements are cooler than that through the winter.
A worked example
Here is a 1,000 square foot basement at about 80 percent humidity, replacing an old 70 pint unit. These lines come from the same chart the calculator above reads.
1,000 sq ft, very damp, replacing an old 70 pint unit
- Under 2,000 sq ft, very damp: 25 to 40 pints a day
- An old 70 pint label today: about 40 to 45 pints
So the old unit's replacement sits right at the top of the range, and it is a good match. This is where the labels confuse people. A shop shelf of 50 pint units looks like a step down from your old 70, but on today's test, a new 50 pint unit is larger than your old one was. To see what it costs to run, use the electricity cost calculator, and if the basement is becoming a room, the basement finishing cost calculator.
Dehumidifier size by room
This is ENERGY STAR's chart in full, and there is no finer version we could source. Pick the top of a range if you are in doubt, as ENERGY STAR says it is better to oversize than undersize.
| How damp | Under 2,000 sq ft | Over 2,000 sq ft |
|---|---|---|
| Slightly to moderately damp, 50 to 75% | 20 to 30 | 30 or more |
| Very damp, 75 to 90% | 25 to 40 | 40 or more |
| Wet, 90 to 100% | 30 to 50 | 50 or more |
| Old label | New label |
|---|---|
| 30 pints | 20 pints |
| 40 pints | 25 pints |
| 50 pints | 30 pints |
| 55 pints | 30 to 35 pints |
| 60 pints | 35 pints |
| 70 pints | 40 to 45 pints |
| 90 pints | 55 pints |
Mistakes that buy the wrong dehumidifier
- Comparing old labels with new. A new 45 pint unit may match an old 70. The test changed, not the machine's ability.
- Mixing up test conditions. Whole-house specs may be rated at 80 degrees and portable ones at 65, so the numbers are not directly comparable.
- Treating it like an air conditioner. Oversizing an air conditioner is a mistake. For a dehumidifier, ENERGY STAR says the opposite.
- Running it cold. Below 65 degrees, a standard unit can frost up. Get one rated for it.
- Leaving the door open. The unit will try to dry the whole house and run all day.
Questions
What size dehumidifier do I need for a 1000 sq ft basement?
About 20 to 30 pints a day if it is slightly damp, 25 to 40 if very damp, and 30 to 50 if wet, by ENERGY STAR's chart for rooms under 2,000 square feet. Its chart has only those two size bands, so area matters less than how damp it is.
Why did dehumidifier pint ratings change?
Because the test changed. Portable units are now rated at 65 degrees and not 80, and new standards took effect in June 2019, so labels from about 2020 show lower numbers for the same machine. An old 70 pint unit is roughly a new 40 to 45 pint unit.
How many pints is good for a dehumidifier?
A range of 20 to 50 pints a day covers most rooms under 2,000 square feet, by how damp they are. Check that you are comparing new labels with new labels. An old unit's number will look much bigger than today's for the same job.
Is it better to oversize a dehumidifier?
Yes. ENERGY STAR says it is better to oversize than undersize, which is the opposite of the advice for an air conditioner. A larger unit does not have to run as hard to reach the same humidity.
What humidity should I aim for?
Between 30 and 50 percent, which ENERGY STAR calls the optimum for a building. A cheap hygrometer will tell you where you are, and most dehumidifiers have a setting that turns them off when they get there.
Can I use one in a cold basement or a crawl space?
Not a standard unit below about 65 degrees, as frost can form on the coils. ENERGY STAR says to consider a unit specified for lower temperatures. Crawl spaces are not covered by this chart, so ask a professional about one of those.
This dehumidifier size is a rule of thumb from ENERGY STAR's chart, which gives ranges and only two room sizes. Temperature and how the room is sealed change what you need, and standard units struggle below 65 degrees, when frost can form. The manufacturer's specification settles it, and units for a full house should be sized by a professional.
Sources and review
- Dehumidifiers, ENERGY STAR, specification effective 2025.
- Dehumidifier testing and capacity, ENERGY STAR, table as of 2020.
- Energy conservation program: test procedure for dehumidifiers, U.S. Department of Energy, 2023.
Checked in November 2026. Spotted a wrong number? Report it and it goes in the corrections log.
How this is calculated
Every figure below is read from the code that produces the answer, so what is written here is what the calculator ran. The constants were last checked against their sources in November 2026.
The arithmetic
Size
Pints a day = the row for your dampness, in the column for your room size
- Dampness
- Slightly damp, very damp or wet, by ENERGY STAR's humidity bands
- Room size
- Under or over 2,000 square feet
Worked through: Very damp, 1,000 sq ft: 25 to 40 pints
The constants, and where they come from
PINTS_CHART
Published figureCapacity in pints per day, by how damp the room is and its size
- damp
- small 20, 30, large 30
- veryDamp
- small 25, 40, large 40
- wet
- small 30, 50, large 50
Applies to: Portable units on the current test. Whole-home units should be sized by a professional
Source: Dehumidifiers, ENERGY STAR, published 2025-10, read 2026-11.
ENERGY STAR's chart has three conditions and gives a range, not a single size. Above 2,000 square feet it gives a minimum.
LARGE_ROOM_SQ_FT
Published figureThe size where ENERGY STAR's chart changes, in square feet
Applies to: The chart's two room sizes
Source: Dehumidifiers, ENERGY STAR, published 2025-10, read 2026-11.
The chart lists under 2,000 and over 2,000 only. We read no primary source with finer steps, so none is offered.
OLD_TO_NEW
Published figureAn old pint label, and the current label it roughly matches
- 30
- 20, 20
- 40
- 25, 25
- 50
- 30, 30
- 55
- 30, 35
- 60
- 35, 35
- 70
- 40, 45
- 90
- 55, 55
Applies to: Portable units. It is a rough correlation
Source: Dehumidifier testing and capacity, ENERGY STAR, published 2020, read 2026-11. This source is about 6 years old, and it is the one the figure rests on.
Portable units are now tested at 65 degrees and not 80, so the same machine carries a lower number. The table is labelled as of 2020.
What the labels mean
- Published figure:
- taken directly from the source named beside it.
If a figure here looks wrong, it may be. Tell us what you found and we will check it against the source and publish a correction if it needs one. How constants are chosen and how often they are reviewed is set out in our methodology.
How to use the dehumidifier size calculator
- 1
Measure the room's area
- 2
Check the humidity, or judge how damp it is
- 3
Read the pints a day to look for
- 4
If you are replacing an old unit, see what its label means today
- 5
Err on the larger side, which ENERGY STAR says is better here
What this calculator assumes
Every estimate here rests on the assumptions below. Where your job differs from one of them, the figure will differ too.
- A portable unit, using the current test at 65 degrees
- ENERGY STAR has only two room sizes, split at 2,000 square feet, so there are no finer steps
- Over 2,000 square feet the chart gives a minimum, with no upper figure
- The old to new label match is ENERGY STAR's rough correlation, and it is not exact
Pro tips
- Keep doors and windows closed while it runs
- Run a hose to a drain so that you do not have to empty the bucket
- Deal with the water getting in, as a dehumidifier does nothing about a leak