What size dehumidifier do you need? Measure the room’s square footage, check the current relative humidity, and match pints per day to how damp the space is. For most rooms under 2,000 square feet, ENERGY STAR points to 20 to 30 pints for slightly damp spaces, 25 to 40 for very damp ones, and 30 to 50 for wet ones.
Size by dampness, not by room name alone. A wet 500-square-foot basement can need more capacity than a mildly humid 1,200-square-foot living area. Fix the water source too, since a dehumidifier controls moisture but does not stop a leak.
What Size Dehumidifier Do You Need?
Capacity is listed in pints removed per 24 hours under standardized test conditions. ENERGY STAR’s sizing guidance for portable units uses both room size and dampness level.
| Room condition without a dehumidifier | Typical signs | Under 2,000 sq. ft. | Over 2,000 sq. ft. |
|---|---|---|---|
| Slightly to moderately damp | Intermittent musty odor; about 50-75% RH | 20-30 pints/day | 30+ pints/day |
| Very damp | Consistently damp feel and smell; damp spots on walls or floors; about 75-90% RH | 25-40 pints/day | 40+ pints/day |
| Wet | Sweating walls or floors, seepage, or laundry drying; about 90-100% RH | 30-50 pints/day | 50+ pints/day |
ENERGY STAR advises oversizing rather than undersizing. If you are replacing a unit, you can also estimate the capacity you need from how much water you empty from the old one each day.
Note on older ratings: Since 2019, DOE tests portable dehumidifiers at 65°F instead of 80°F to better match basement conditions. ENERGY STAR says that makes the same unit report lower capacity, and it lists an old 70-pint rating as roughly 40 to 45 pints under the newer ratings. Actual changes vary by model.
How to Size a Dehumidifier Step by Step
- Find the room size. Multiply length by width in feet. A 20 by 15 foot room is 300 square feet.
- Measure humidity. Use a hygrometer before you turn the dehumidifier on.
- Classify the dampness. Slightly damp, very damp, or wet, using the table above.
- Pick the capacity range. Use the column for your room size.
- Add headroom. Move up a size if moisture returns quickly, the room is cold, ceilings are high, or the unit will handle laundry or other wet materials.
Measure Your Room Footage
| Measurement | Why it matters |
|---|---|
| Length x width | Gives the square footage used for the capacity baseline. |
| Ceiling height | Tall rooms hold more air, so they may need extra capacity. |
| Open doors or connected rooms | The unit may end up treating all the connected air, not just one room. |
| Moisture sources | Showers, laundry, foundation seepage, wet materials, and indoor plants add to the load. |
In an open floor plan, measure the full area that shares air with the dehumidifier. Closing a door can help a smaller unit by limiting new humid air.
Check Humidity With a Hygrometer
A hygrometer shows relative humidity (RH). The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. ENERGY STAR notes that anything above 50 percent may promote mold growth.
Place the hygrometer away from windows, vents, sinks, showers, and cold corners, and let it settle before you trust the reading. For problem rooms, check at different times of day, since humidity often rises after showers, cooking, laundry, rain, or watering plants.
Warning: If you see active leaks, standing water, sewage backup, or widespread visible mold, do not rely on a dehumidifier alone. Stop the water source, dry wet materials quickly, and call a qualified professional when the problem is large or recurring.
Match Pint Capacity to Moisture Load
Square footage gives you the starting point, and moisture load tells you whether to move up. A bathroom, laundry room, basement, or plant room can need more capacity than a dry bedroom of the same size.
Bedrooms, Bathrooms, and Living Rooms
For a slightly damp room under 2,000 square feet, the 20 to 30 pint range is the usual starting point. Move to 25 to 40 pints if the room smells musty, shows condensation, or has damp spots. For a wet room or one used to dry laundry, use 30 to 50 pints. Our room guides cover the details for a bedroom and a bathroom.
Basements
Basements often need more capacity because concrete, foundation walls, floor cracks, and limited ventilation can keep adding moisture. A very damp small-to-medium basement falls in the 25 to 40 pint range. A wet basement, or one over 2,000 square feet, calls for 50+ pints or a whole-home system. See the basement size chart for more.
Laundry, Drying Areas, and Plant Rooms
These spaces add water to the air. If you know how much water evaporates in a day, convert it to pints: 1 gallon equals 8 pints. Pick a unit that can remove that amount with a buffer for peak humidity.
| Moisture source | Sizing tip |
|---|---|
| Watering indoor plants | Estimate how much water evaporates into the room, and add capacity if RH spikes after watering. |
| Drying wet laundry indoors | Use a closed room, good airflow, and continuous drainage if laundry is frequent. |
| High-occupancy rooms | People, pets, and frequent door opening add humidity, so a slightly larger unit may run more steadily. |
Tip: If your number falls between two sizes, choose the larger unit with a built-in humidistat. It can shut off when the target RH is reached, while an undersized unit may run constantly and still leave the room damp.
Choose the Right Pint Capacity
The best capacity is the smallest unit that can hold your target humidity without running nonstop. Slightly oversized is usually better than undersized when a room has recurring dampness.
- Room size: Larger rooms hold more air and usually need more moisture removal, but a 300-square-foot room with wet walls can need more than a 900-square-foot room that is only slightly humid.
- Moisture level: Use the hygrometer reading and the symptoms together. If the room sits just above target and feels slightly sticky, start low. If it smells musty or has damp spots, move up. If walls or floors sweat, treat it as a wet space.
- Changing conditions: Add capacity for high ceilings, poor air sealing, frequent door opening, laundry drying, wet concrete, a sump area, or humidity that returns quickly after the unit shuts off.
Larger spaces have their own guides, such as the 2,000 square foot size guide, and small homes can check the apartment size guide.
Pick a Dehumidifier for Cold Rooms
Compressor-style dehumidifiers generally remove less water as the room gets colder, and coils can frost. Check the operating temperature range in the manual before you buy. For example, the Midea MAD50S1QWT manual lists an operating range of 41 to 95°F, says to keep the room at or above 41°F, and notes that frost on the coils at lower temperatures can reduce performance.
For an unheated garage, basement, shed, or storage room, consider:
- Low-temperature compressor model: suits a cool room that stays within the manual’s range.
- Auto-defrost: helps when coils may frost in cold weather.
- Desiccant dehumidifier: can work in colder spaces, though it may use more energy and add some heat.
- Whole-home or ducted unit: better when humidity affects several rooms or a portable unit cannot hold the space. The garage size guide covers unheated spaces in more detail.
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When a Large Unit Makes Sense
A large-capacity unit fits a wet room, a space over 2,000 square feet, a laundry-drying area, or a space connected to a damp crawl space. It also fits when a smaller unit runs all day and RH stays above target.
Pair a large unit with continuous drainage if you expect daily use. Many portable units stop automatically when the bucket is full, and moisture control stops with them.
Avoid Common Sizing Mistakes
- Buying by room name only. Measure square footage and RH instead.
- Ignoring leaks. A dehumidifier cannot keep up forever with a roof leak, plumbing leak, or foundation seepage.
- Blocking airflow. The Midea manual calls for at least 8 inches of space on all sides and at least 16 inches at the air outlet; check your own manual for your model.
- Using the wrong drain setup. A full bucket stops the unit. Use a hose, floor drain, sump, or pump when daily removal is high.
- Setting RH too low. Aim for the 30 to 50 percent range while staying below 60 percent.
- Forgetting the filter. A clogged filter reduces airflow and effectiveness.
Choose Features That Save Time
Recommended Products
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Drain Options
Most portable units use a removable bucket with an automatic shutoff when full. ENERGY STAR notes that some models have a hose fitting so water can drain to a floor drain or sump, and advises keeping the unit near the drain so the hose stays short. A built-in pump helps when water must move up to a sink or higher drain. Keep drain hoses away from cords and electrical connections.
Other Features
Look for a built-in humidistat, auto-restart, full-bucket shutoff, a hose connection, a filter that is easy to reach, and ENERGY STAR certification. ENERGY STAR criteria use Integrated Energy Factor (IEF) to compare moisture removal with energy use.
Setup Checklist
- Place the unit on a level surface.
- Keep windows and exterior doors closed while it runs.
- Keep the intake and exhaust clear.
- Clean the filter as the manual recommends.
- Check the drain hose for kinks, clogs, or poor slope.
- Compare the built-in humidistat with a separate hygrometer.
When to Upgrade to a Whole-Home System
ENERGY STAR describes whole-home dehumidifiers as ducted, usually permanent units that suit humid climates with central air conditioning, especially where humidity stays above 55 percent throughout the house. It recommends hiring a contractor to size and install one. Consider it when:
- Several rooms stay above target RH.
- Portable buckets fill too quickly.
- The basement is dry but the upstairs still feels sticky.
- You want humidity control without visible machines in living areas.
Troubleshooting After You Size the Unit
| Problem | Likely cause | Fix |
|---|---|---|
| Unit runs nonstop | Too much moisture entering, or capacity too low | Fix leaks, close outside air paths, clean the filter, or size up. |
| Bucket fills quickly | Room is very damp or wet | Use continuous drainage or a pump. |
| RH does not drop | Poor airflow, open windows, or inaccurate built-in sensor | Move the unit, close openings, and compare with a separate hygrometer. |
| Coils frost | Room may be below the operating range | Warm the room, use auto-defrost, or choose a low-temperature model. |
| Musty smell returns | Hidden moisture source | Inspect for leaks, wet carpet, damp drywall, and poor drainage. |
For more on what a normal day looks like, see how much water a dehumidifier should collect per day.
Related Guides
- Basement dehumidifier size chart
- Bedroom dehumidifier size guide
- Bathroom dehumidifier size guide
- Garage dehumidifier size guide
- Dehumidifier size for 2,000 square feet
Frequently Asked Questions
Is it better to oversize or undersize a dehumidifier?
It is usually better to oversize slightly, and ENERGY STAR advises oversizing rather than undersizing. An undersized unit may run constantly and still fail to lower humidity. A slightly larger unit with a humidistat can shut off once the target RH is reached.
How big of a dehumidifier do I need for 1,200 square feet?
Start with the moisture level. If the space is slightly to moderately damp, 20 to 30 pints per day may work. If it is very damp, choose 25 to 40 pints. If it is wet, has seepage, or is used for drying laundry, choose 30 to 50 pints and plan for continuous drainage.
What size dehumidifier do I need for a basement?
A small-to-medium basement that is slightly damp may need 20 to 30 pints per day. A very damp one usually needs 25 to 40 pints, and a wet one 30 to 50. If the basement is over 2,000 square feet or moisture affects the whole house, consider 50+ pints or a whole-home system.
What humidity setting should I use on a dehumidifier?
Aim for 30 to 50 percent RH, which is the range both the EPA and ENERGY STAR describe. In heating season in a cold climate, ENERGY STAR suggests 30 to 40 percent to reduce window condensation. Use a separate hygrometer to confirm the real room reading.
Why are newer dehumidifier pint ratings lower than older ones?
Portable units are now tested at 65°F instead of 80°F, which better reflects basement conditions. The cooler test lowers the reported capacity of the same unit, so a current label can look smaller than an older one. ENERGY STAR lists an old 70-pint rating as roughly 40 to 45 pints today.
Should I use a dehumidifier if I have COPD?
Controlling damp air, mold, and musty odors may make a home more comfortable, but COPD care should be guided by your clinician. Avoid both very damp and very dry air, use a hygrometer, and ask your healthcare provider which humidity range is right for you.
Sources
- U.S. EPA: A Brief Guide to Mold, Moisture and Your Home
- ENERGY STAR: Dehumidifiers
- ENERGY STAR: Dehumidifier Testing and Capacity
- ENERGY STAR: Dehumidifiers Key Efficiency Criteria
- Midea MAD50S1QWT Dehumidifier Manual
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