What size dehumidifier do I need for my basement?

Multiply the length by the width, judge how damp the space is, and read the AHAM / ENERGY STAR chart. A 25 × 30 ft basement is 750 sq ft; very damp, the chart gives 14.5 pints per day on the old scale, so 15 pints/day for an older-rated unit or 10 pints/day for one with the 2019+ rating. A 20-pint unit is the smallest common size above that.

Why do new dehumidifiers have lower pint ratings than old ones?

The US Department of Energy changed its test procedure. Portable dehumidifiers used to be rated at 80°F and 60% relative humidity; the current procedure (appendix X1, from a 2015 final rule, with efficiency standards from June 2019 and the lower labels seen from early 2020) uses 65°F and 60%, which is nearer a basement. Cooler air holds less water, so there is less to remove and the same machine gets a smaller number. ENERGY STAR expects the capacity of the same dehumidifier to be lower under the new procedure, and its rough correlation is about 30 old pints = 20 new, 50 = 30 and 70 = 40 to 45. Nothing about the machine changed, only the test.

Should I use the old or the new rating?

Use the one on the unit you are looking at. If its label or spec sheet shows the 2019+ DOE rating, choose “2019+” here; for an older label, an old listing or a used machine, choose “pre-2019”. The same 25 × 30 ft very damp basement is 10 pints/day on the 2019+ scale and 15 pints/day on the old one. Comparing a new-rated unit with an old-chart figure makes a machine look about a third too small.

What if my room is not exactly 500, 1,000 or 1,500 sq ft?

This tool reads a straight line between the chart’s columns: a 30 × 40 ft basement, 1,200 sq ft, is 40% of the way from the 1,000 to the 1,500 sq ft column. For a wet space the chart gives 22.4 pints per day there, 23 pints/day on the old rating and 15 pints/day on the 2019+ one. Below 500 sq ft it uses the 500 sq ft value without scaling down: a 300 sq ft very damp room is 12 old pints, 8 pints/day on the 2019+ rating.

What if my space is bigger than 2,500 sq ft?

The chart ends at 2,500 sq ft, and this tool does not extend it. Above that it shows “at least” the 2,500 sq ft value, such as at least 21 pints/day (beyond the chart) for 3,000 sq ft, and a warning: that is a minimum, not a size. Use more than one dehumidifier in different zones, or a whole-house unit that connects to the ducts, and have an HVAC professional size it.

How do I tell how damp my space is?

The chart has four levels. Moderately damp: it feels damp and smells musty only in humid weather. Very damp: it always feels damp and smells musty, and there are damp spots on the walls or floor. Wet: it feels and smells wet and the walls or floor sweat, or there are signs of seepage. Extremely wet: there is standing water or seepage, or laundry is dried in the space. These descriptions are this site’s plain-word summaries. A cheap hygrometer helps: a space that sits above about 60% relative humidity is a mould risk. If you are between two levels, take the damper one.

Is a bigger dehumidifier always better?

Not always, but for dehumidifiers, going one size up is safer than going one size down. A unit that is too small runs all day and may never reach a healthy humidity (30% to 50%). One that is a little large reaches it sooner, then cycles off. Do not jump several sizes, which costs more to buy and to run. If the space floods or seeps, no dehumidifier is the fix: repair the water source first.

Does the chart include ceiling height, laundry or a leak?

No. The chart only looks at floor area and how damp the space is, and was written for ordinary ceilings. A high ceiling, an open stairwell, drying laundry, a bathroom without a fan or a crawl space with bare soil all add moisture or air to treat. The “extremely wet” row is the nearest the chart comes to it, and a leak or standing water is a drainage problem first. Add the floor area of an open adjoining space in “Extra area”.

How do I add an adjoining space?

Enter its floor area in “Extra area”, and it is added to length × width. A 25 × 30 ft basement with a 250 sq ft finished area open to it is 1,000 sq ft: very damp, 12 pints/day on the 2019+ scale. A space that is closed off, such as a room behind a door, is better treated as its own room.

Why is the chart not from energystar.gov directly?

The numbers here are the AHAM sizing chart as printed in copies from Cornell Cooperative Extension, an energy-utility blog and a manufacturer brochure, and they agree with each other. This site could not read ENERGY STAR’s current page in full, which has its own room-size and dampness chart, so it is marked as unverified. If a figure matters for a purchase, compare it with the current ENERGY STAR page and with the maker’s own sizing guide for the model.

Dehumidifier Size Calculator: How Many Pints Per Day Do I Need?

A 25 × 30 ft basement is 750 sq ft. For a very damp space the AHAM / ENERGY STAR chart gives 14.5 pints per day (read between its 500 and 1,000 sq ft columns), which is 15 pints/day on the old pre-2019 rating and 10 pints/day on the 2019+ DOE rating that units are labelled with now. The smallest common size at or above that is a 20-pint unit. Enter the room size, how damp it is and which rating scale you are comparing to adjust that. Rooms over 2,500 sq ft are beyond the chart: use more than one unit or a whole-house dehumidifier.

Figures based on the sources listed belowUpdated 2026-10-15How we calculate

Room length

Room width

Extra area (optional) (sq ft)

Floor area of an open adjoining space the unit also has to dry, such as a laundry nook or a second part of the basement, added to length × width. Leave 0 for a closed room.

How damp is the space?The chart rows: judge the space before any dehumidifier is running. When unsure between two, take the damper one.

Capacity rating on the unitThe chart is on the old 80°F scale. Since the DOE test moved to 65°F the same machine is labelled with a smaller number, so pick the scale of the unit you are comparing.

10 pints/day

AHAM chart cell: between 500 sq ft (12) and 1,000 sq ft (17), very damp: 14.5 pints (your area: 750 sq ft)
Rating basis: 2019+ DOE rating (65°F test): the chart’s 14.5 pints converted to 10 pints
Nearest common size: 20-pint unit (smallest common size at or above 10)

Shopping list

Dehumidifier with pump
Hygrometer (humidity monitor)
Dehumidifier drain hose
Moisture meter
Tape measure (25 ft)

Show diagram

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AHAM / ENERGY STAR dehumidifier sizing chart (pre-2019 rating)

Pints per day by area and how damp the space is, on the old 80°F scale (chart, pre-2019 (80°F)). Between the columns this calculator reads a straight line; below 500 sq ft it uses the first column, and above 2,500 sq ft it shows a minimum and says to use more than one unit. Read from copies of the chart, not from energystar.gov.
Conditions	500 sq ft	1,000 sq ft	1,500 sq ft	2,000 sq ft	2,500 sq ft
Moderately damp	10	14	18	22	26
Very damp	12	17	22	27	32
Wet	14	20	26	32	38
Extremely wet	16	23	30	37	44

The same chart on the 2019+ DOE rating (65°F)

The chart values converted with ENERGY STAR’s old-to-new correlation, rounded up to a whole pint. An estimate: the real change differs by model.
Conditions	500 sq ft	1,000 sq ft	1,500 sq ft	2,000 sq ft	2,500 sq ft
Moderately damp	7	10	12	15	18
Very damp	8	12	15	18	21
Wet	10	14	18	21	24
Extremely wet	11	16	20	24	27

Old rating to 2019+ rating (ENERGY STAR correlation, portable units)

The rough correlation this calculator interpolates. ENERGY STAR gives 30 to 35 for 55 and 40 to 45 for 70; the middle is shown.
Old rating (80°F), pints/day	2019+ rating (65°F), pints/day
30	20
40	25
50	30
55	32.5
60	35
70	42.5
90	55

Dehumidifier size for common rooms by dampness

Pints per day worked by this calculator, written as 2019+ rating / pre-2019 rating, for the room alone with no extra area.
Room	Sq ft	Moderately damp	Very damp	Wet	Extremely wet
Damp bedroom or office, 12 × 14 ft	168	7 / 10	8 / 12	10 / 14	11 / 16
Basement room, 20 × 25 ft	500	7 / 10	8 / 12	10 / 14	11 / 16
Half a basement, 25 × 30 ft	750	8 / 12	10 / 15	12 / 17	13 / 20
Whole basement, 30 × 40 ft	1,200	11 / 16	13 / 19	15 / 23	18 / 26
Large basement, 40 × 50 ft	2,000	15 / 22	18 / 27	21 / 32	24 / 37

Methodology & assumptions

This follows the AHAM / ENERGY STAR dehumidifier sizing chart, in four steps. 1) Area = length × width, plus any extra open area you enter, in sq ft. 2) Chart value = pints per day for that area and dampness, from the chart below: columns at 500, 1,000, 1,500, 2,000 and 2,500 sq ft, rows for moderately damp, very damp, wet and extremely wet. Interpolation rule: between two columns the value is read on a straight line (750 sq ft, very damp, is halfway between 12 and 17 pints, so 14.5). Below 500 sq ft the 500 sq ft column is used as it is, not scaled down, because the chart has nothing smaller and a small, damp room still needs a real machine. Above 2,500 sq ft the chart ends: the result is shown as “at least” the 2,500 sq ft value, as a minimum and not a size, with advice to use more than one unit or a whole-house dehumidifier, and no extrapolation is made. 3) Rating basis. The chart is on the old scale, in which a dehumidifier was tested at 80°F and 60% relative humidity. The US Department of Energy’s current test procedure (appendix X1, from the 2015 final rule, with the new efficiency standards applying from June 2019 and the lower labels appearing on shelves from early 2020) tests portable units at 65°F and 60%, a cooler basement-like condition in which there is less water to remove. The same machine therefore carries a smaller number: ENERGY STAR’s rough correlation is about 30 pints old = 20 new, 40 = 25, 50 = 30, 60 = 35, 70 = 42.5 (the midpoint of its 40 to 45), 90 = 55. For the 2019+ rating this tool converts the chart value along that correlation, in a straight line between its rows; below 30 old pints, where the correlation has no row, it keeps the 30-to-20 ratio (two thirds), which is an extrapolation and an estimate. The pre-2019 setting leaves the chart value as it is. 4) The result is rounded up to a whole pint, and the nearest common size is the smallest size at or above it from a list of typical labelled sizes (20, 22, 25, 30, 35, 40, 50, 60, 70 for 2019+ ratings; 20, 25, 30, 35, 40, 45, 50, 60, 70 for older ones). That size list is an estimate of what is sold, not a standard. The conversion is approximate and ENERGY STAR says the real change varies by model, so check the number on the unit you are looking at: if it is labelled with the 2019+ DOE rating, use the 2019+ answer, and if it is an older label or an old listing, use the pre-2019 one. ENERGY STAR’s own current page also gives a chart by room size and dampness; the numbers here are the AHAM version read from copies of it, which this site could not compare line by line with the current page, so treat the cell values as a typical figure and not a guarantee. What this is not: a moisture-load calculation. Ceiling height, a leak, laundry, a crawl space, climate and the temperature of the room all change what you need, and a unit that runs constantly cannot fix a water source: stop the moisture entering, then dehumidify. Sizing up is better than down: a unit that is too small runs all day without reaching a healthy humidity (aim for 30% to 50%).

ENERGY STAR, Dehumidifier Testing and Capacity: portable dehumidifiers are tested at 65°F rather than 80°F so that the capacity reflects a basement, a given machine is expected to carry a smaller capacity number, and the rough old-to-new correlation (about 30 pints old = 20 new, 50 = 30, 70 = 40 to 45, 90 = 55)
ENERGY STAR, Dehumidifiers: the product page, with its own sizing chart by room size and dampness (not used for the numbers here; this site could not read it directly, see the note below)
US Department of Energy, Energy Conservation Program: Test Procedures for Dehumidifiers, final rule of June 2015 (dehumid_tp_finalrule_0.pdf): the new dry-bulb temperature conditions (appendix X1 to 10 CFR 430 subpart B) for portable and whole-home dehumidifiers
Green Building Advisor, The Confusing World of Dehumidifier Capacity: a unit rated at 30 pints per day under the old procedure is a 20 pints per day unit under the new one, and why the numbers are not comparable
Selecting a Dehumidifier (Cornell Cooperative Extension, Schuyler County), a copy of the AHAM sizing chart: 500 to 2,500 sq ft against four dampness levels, in pints per 24 hours. The same values appear on the Direct Energy blog (What Do I Need to Know When Shopping for a Dehumidifier?) and in an AJ Madison D50BP brochure
Unverified: the plain-words descriptions of the dampness levels, the 2019+ conversion below 30 pints, the middle of ENERGY STAR’s ranges for 55 and 70 pints, and the list of common unit sizes are this site’s summaries and estimates, not figures from a manufacturer data sheet or from energystar.gov text read directly. The chart values themselves were found on secondary copies, not on the energystar.gov page

How to size a dehumidifier

Measure the space. Measure the length and width in feet and multiply to get square feet. Add the floor area of any open adjoining space the unit also has to dry.
Judge how damp it is. Pick moderately damp, very damp, wet or extremely wet from how the space feels, smells and looks before any dehumidifier runs.
Read the chart. Find the area and dampness in the AHAM / ENERGY STAR chart, reading a straight line between the 500, 1,000, 1,500, 2,000 and 2,500 sq ft columns. Above 2,500 sq ft use more than one unit.
Match the rating scale. The chart is on the old 80°F scale. For a unit labelled with the 2019+ DOE rating (65°F), convert it: about 30 old pints is 20 new, 50 is 30, 70 is 40 to 45.
Choose a unit. Pick the smallest common size at or above the result, and fix any water source first: a dehumidifier does not cure a leak.

Worked examples

Project	Result
25 × 30 ft basement, very damp, 2019+ rating	10 pints/day (750 sq ft, 14.5 chart pints, 20-pint unit)
The same basement on the pre-2019 rating	15 pints/day (20-pint unit)
20 × 25 ft room, moderately damp (exactly 500 sq ft)	7 pints/day (500 sq ft, moderately damp: 10 pints (your area: 500 sq ft))
15 × 20 ft room, very damp (under 500 sq ft)	8 pints/day (first column, 12 chart pints)
30 × 40 ft basement, wet, pre-2019 rating	23 pints/day (1,200 sq ft, 22.4 chart pints)
The same wet basement, 2019+ rating	15 pints/day (20-pint unit)
40 × 50 ft basement, extremely wet (2,000 sq ft)	24 pints/day (37 chart pints, 25-pint unit)
25 × 30 ft basement with a 250 sq ft open area, very damp	12 pints/day (1,000 sq ft, 17 chart pints)
60 × 50 ft space, very damp (3,000 sq ft, beyond the chart)	at least 21 pints/day (beyond the chart): use more than one unit or a whole-house dehumidifier

Frequently asked questions

What size dehumidifier do I need for my basement?: Multiply the length by the width, judge how damp the space is, and read the AHAM / ENERGY STAR chart. A 25 × 30 ft basement is 750 sq ft; very damp, the chart gives 14.5 pints per day on the old scale, so 15 pints/day for an older-rated unit or 10 pints/day for one with the 2019+ rating. A 20-pint unit is the smallest common size above that.
Why do new dehumidifiers have lower pint ratings than old ones?: The US Department of Energy changed its test procedure. Portable dehumidifiers used to be rated at 80°F and 60% relative humidity; the current procedure (appendix X1, from a 2015 final rule, with efficiency standards from June 2019 and the lower labels seen from early 2020) uses 65°F and 60%, which is nearer a basement. Cooler air holds less water, so there is less to remove and the same machine gets a smaller number. ENERGY STAR expects the capacity of the same dehumidifier to be lower under the new procedure, and its rough correlation is about 30 old pints = 20 new, 50 = 30 and 70 = 40 to 45. Nothing about the machine changed, only the test.
Should I use the old or the new rating?: Use the one on the unit you are looking at. If its label or spec sheet shows the 2019+ DOE rating, choose “2019+” here; for an older label, an old listing or a used machine, choose “pre-2019”. The same 25 × 30 ft very damp basement is 10 pints/day on the 2019+ scale and 15 pints/day on the old one. Comparing a new-rated unit with an old-chart figure makes a machine look about a third too small.
What if my room is not exactly 500, 1,000 or 1,500 sq ft?: This tool reads a straight line between the chart’s columns: a 30 × 40 ft basement, 1,200 sq ft, is 40% of the way from the 1,000 to the 1,500 sq ft column. For a wet space the chart gives 22.4 pints per day there, 23 pints/day on the old rating and 15 pints/day on the 2019+ one. Below 500 sq ft it uses the 500 sq ft value without scaling down: a 300 sq ft very damp room is 12 old pints, 8 pints/day on the 2019+ rating.
What if my space is bigger than 2,500 sq ft?: The chart ends at 2,500 sq ft, and this tool does not extend it. Above that it shows “at least” the 2,500 sq ft value, such as at least 21 pints/day (beyond the chart) for 3,000 sq ft, and a warning: that is a minimum, not a size. Use more than one dehumidifier in different zones, or a whole-house unit that connects to the ducts, and have an HVAC professional size it.
How do I tell how damp my space is?: The chart has four levels. Moderately damp: it feels damp and smells musty only in humid weather. Very damp: it always feels damp and smells musty, and there are damp spots on the walls or floor. Wet: it feels and smells wet and the walls or floor sweat, or there are signs of seepage. Extremely wet: there is standing water or seepage, or laundry is dried in the space. These descriptions are this site’s plain-word summaries. A cheap hygrometer helps: a space that sits above about 60% relative humidity is a mould risk. If you are between two levels, take the damper one.
Is a bigger dehumidifier always better?: Not always, but for dehumidifiers, going one size up is safer than going one size down. A unit that is too small runs all day and may never reach a healthy humidity (30% to 50%). One that is a little large reaches it sooner, then cycles off. Do not jump several sizes, which costs more to buy and to run. If the space floods or seeps, no dehumidifier is the fix: repair the water source first.
Does the chart include ceiling height, laundry or a leak?: No. The chart only looks at floor area and how damp the space is, and was written for ordinary ceilings. A high ceiling, an open stairwell, drying laundry, a bathroom without a fan or a crawl space with bare soil all add moisture or air to treat. The “extremely wet” row is the nearest the chart comes to it, and a leak or standing water is a drainage problem first. Add the floor area of an open adjoining space in “Extra area”.
How do I add an adjoining space?: Enter its floor area in “Extra area”, and it is added to length × width. A 25 × 30 ft basement with a 250 sq ft finished area open to it is 1,000 sq ft: very damp, 12 pints/day on the 2019+ scale. A space that is closed off, such as a room behind a door, is better treated as its own room.
Why is the chart not from energystar.gov directly?: The numbers here are the AHAM sizing chart as printed in copies from Cornell Cooperative Extension, an energy-utility blog and a manufacturer brochure, and they agree with each other. This site could not read ENERGY STAR’s current page in full, which has its own room-size and dampness chart, so it is marked as unverified. If a figure matters for a purchase, compare it with the current ENERGY STAR page and with the maker’s own sizing guide for the model.

Handy tools

Heat Index and Wind Chill Calculator: Humidity and temperature together set how hot it feels. It turns both into the NWS heat index and the dew point.
Feet and Inches Calculator: Measured 12' 7 1/2"? It turns tape readings into the decimal feet the room fields take.