How-to · Air & Climate
What Size Dehumidifier Do I Need? (Pints, Room Size and Dampness)
Short answer: Measure the room, decide how damp it is, and match the two to a pint rating. A small bedroom or bathroom that only feels sticky needs a 20- to 22-pint unit. A damp basement or a large living area needs 35 pints or more. When you are between sizes, go up, not down.
What the pint rating means
Dehumidifiers are sold by how many pints of water they can remove from the air in 24 hours. The number comes from a standard test, not from your house, so treat it as a way to compare models rather than a promise. One wrinkle: the US test method changed in 2019 to use a cooler, less humid room, so today’s ratings are smaller than older ones for the same machine. A unit marked 35 pints now is about what was sold as 50 pints before. If you are comparing an old review with a new box, keep that in mind.
Most consumer units fall into three bands:
| Band | Pints per day (current rating) | Typical use |
|---|---|---|
| Small | 20 to 22 | Bedroom, bathroom, closet, small office |
| Medium | 30 to 35 | Living room, large bedroom, small basement |
| Large | 40 to 50 | Basement, open-plan floor, very damp spaces |
Step 1: Measure the room
Multiply the length by the width to get square feet. A 12 by 14 foot bedroom is about 170 square feet; a 25 by 30 foot basement is 750. If the dehumidifier will serve two rooms with an open doorway between them, add them together, but assume the far room will dry more slowly.
Step 2: Decide how damp it is
Be honest about the room, because this matters as much as size:
- Slightly damp. The air feels heavy in summer, but there is no smell and nothing is wet.
- Damp. A musty smell, condensation on windows, or clothes that take forever to dry.
- Very damp. Visible mold spots, damp patches on walls, or water that has come in from outside.
A cheap hygrometer takes the guessing out of this. Above 60 percent relative humidity is damp; above 70 is very damp.
Step 3: Match size to room
| Room size | Slightly damp | Damp | Very damp |
|---|---|---|---|
| Up to 300 sq ft | 20 pints | 20 to 22 pints | 30 pints |
| 300 to 700 sq ft | 22 pints | 30 to 35 pints | 40 pints |
| 700 to 1,200 sq ft | 30 pints | 35 to 40 pints | 50 pints |
| Over 1,200 sq ft | 35 pints | 50 pints | 50 pints or two units |
These are starting points, not rules. If the room is on the line between two sizes, pick the bigger one. A dehumidifier that is too small runs constantly and never gets the room where you want it; one that is a bit too big reaches the target and switches off, which also saves power.
When to go bigger than the chart says
- The room is a basement or sits partly below ground.
- Someone dries laundry indoors, or the room has a shower without an exhaust fan.
- The climate is humid for most of the year.
- Ceilings are high, which adds air volume the floor area does not show.
- You want the unit to run less often, for noise or electricity reasons.
Features worth paying for
A drain hose connection. Every unit has a tank you empty by hand, and a 20-pint unit in a damp room fills it more than once a day. A hose port lets you run the water to a floor drain and forget about it. In a basement this is the single most useful feature.
A built-in pump. If there is no floor drain and the nearest sink is above the unit, a pump pushes the water up and out. It costs more but saves a daily chore.
A humidistat you can set. Lets you choose a target humidity, so the unit cycles off when the room is right instead of running until the tank is full.
Auto restart. After a power cut, the unit starts again on its own. Important if it runs in a basement you rarely visit.
A washable filter. They all have one; just check that it slides out without tools.
Where to put it
Put the dehumidifier where the damp is worst, with a foot or so of space around the air intake and outlet. Close windows and doors while it runs, or it will try to dry the whole neighborhood. In a basement, place it near the middle of the space rather than against the dampest wall, so air can circulate past it.
Running costs in plain terms
A dehumidifier uses roughly as much power as a small refrigerator while it runs, and the larger the unit, the higher the draw. The trick to keeping the bill down is not a smaller unit but a correctly sized one that reaches its target and cycles off. Units with an Energy Star label pull more water per unit of electricity than those without, which matters if it will run all summer.
Common mistakes
- Buying by price alone and ending up with a 20-pint unit in a 700-square-foot basement.
- Comparing an old 50-pint rating with a new 30-pint rating as if they were the same test.
- Leaving a window open “for fresh air” while the unit runs.
- Forgetting to clean the filter, which cuts airflow and makes the unit work harder.
- Setting the target to 30 percent when 45 to 50 is comfortable and uses far less power.
FAQ
Is a bigger dehumidifier always better?
Not always. A bigger unit pulls water faster and cycles off sooner, which is good, but it costs more, weighs more and is louder when it runs. For a bedroom or a small bathroom, a small unit that runs longer is often the better buy. For a basement or a whole floor, go big.
What does the pint rating on a dehumidifier mean?
It is how many pints of water the unit can pull from the air in 24 hours under a standard test condition. Since 2019 the US test uses a cooler, less humid room than before, so new ratings look smaller than old ones for the same machine. A 35-pint unit today is roughly what used to be sold as 50 pints.
Can one dehumidifier handle a whole house?
A portable unit handles the room it sits in, and a little of the space around it if doors are open. For a whole house with damp on more than one floor, you need either one unit per problem area or a whole-house unit tied into the HVAC system.
What humidity level should I aim for?
Between 30 and 50 percent relative humidity is comfortable and keeps mold and dust mites in check. Most dehumidifiers let you set a target; 45 percent is a good starting point.