How to Size a Dehumidifier

So you need a dehumidifier-

Here's the deal:

It's easy to size a dehumidifier properly with the handy dehumidifier calculator.

Dehumidifier Sizing Calculator

Calculate how many pints you need to dry your room, home, office, or basement.

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If you're wondering how the dehumidifier calculator works, read on...

WARNING! The following information is really dry. If I were you I'd just use the calculator to find out what size dehumidifier you need. CONTINUE READING AT YOUR OWN RISK.

Dehumidifier Sizing

Dehumidifiers are usually rated in pints/day or liters/day, and at different temperatures and relative humidities.

Are you sure you want to learn about these dry topics?
No? Click here to skip to FAQ.

Relative Humidity

This is the % of water in the air out of the total possible water the air could hold at a given temperature and pressure (for normal applications, pressure is varying because of altitude).


A-what?! AHAM is the Association of Home Appliance Manufacturers.
Some manufacturers will verify dehumidifiers at AHAM's standards, which is how many pints the dehumidifier removes in 24 hours at 80/A1/C6F (dry-bulb), 60% relative humidity, and we should assume, 1atm | 14.7psi | 1.01bar of pressure - approximately the pressure of air at sea-level.

Often you'll see a dehumidifier with specs like 100 pints per day, rated something like 70 pints by the AHAM standards.

AHAM requires manufacturers to advertise only the AHAM standard pints per day, but, there's no law requiring manufacturers or resellers to publish AHAM figures, and it's common to see both an AHAM capacity, and another rating in more favorable conditions, so their dehumidifiers can be advertised as higher capacity than the competition.

Why does this all matter?

You probably just want to know what size dehumidifier to get for 500, 1000, 1500 square feet.

Did we have to explain a bunch of thermodynamics crap just to size a dehumidifier?

Well, if you want to know which dehumidifier to get, we have to know
1. the temperature and relative humidity in the space, and
2. the volume, or cubic feet of air that needs dehumidification

So, how can you actually use this?

For temperature and relative humidity:

Some people will actually get a humidity monitor to measure the relative humidity.
It's useful if you need to keep the humidity below a certain %.

For most humidity problems, the calculator lets you approximate relative humidity by how the room looks and feels. If the air feels "muggy" to you, or if you see condensation on the walls, water dripping down the walls, or (heaven help you!) standing water, we've got a good approximation.

For volume:

You could get out a tape measure, and measure length, width, and height of each room you want to dehumidify, (and for big problems most contractors will do that!) but, most ceilings are a very similar height from most floors. Most people know an approximate square footage of their basement.

The calculator takes what most people know, like:
"I've got a 700 square foot basement, and it feels mighty damp."
and puts it in numbers, like:
"10,000 cubic feet at 80% relative humidity, and 50\A1\C6F"

And crunches those numbers to make a recommendation with a margin of safety:
For example, if the calculations say we need 59.4 pints/day capacity,
it'll recommend a 70-pint dehumidifier.

The best part?

You don't have to worry or waste time calculating all this. Just give your best guess for square footage and dampness, and let the dehumidifier calculator do the math for you.

Email the Dehumidifier Guy

Questions & Complaints Welcome!

Tom built the dehumidifier calculator and sells thousands of dehumidifiers every year.

What Size Dehumidifier Do I Need?

The Dehumidifier Size Calculator answers how many pints of capacity you require to dry your basement, bedroom, or home.

For example, you can select a 900 square foot room size, or a room type, like 'large basement', 'small office' or '2 bedrooms'. Then specify damp, really damp, wet, or extremely wet, and the calculator instantly displays how many pints you need, and recommends a properly sized dehumidifier for your basement.

Frequently Asked Questions

Are the dehumidifiers Energy Star efficient?

Yes, all the dehumidifiers recommendations are Energy Star certified. Cheaper to run, easier on the environment.

Is there any downside to ordering a size larger than necessary?

No, I usually recommend a 70-pint dehumidifier over a 50-pint or 30-pint, because it costs just $10 more, the Energy Star rating means it will use less electricity. If you set the desired humidity level, it will power on and off as needed.

Does the Frigidaire 70-pint unit have a built-in pump for uphill water disposal?

It doesn't go uphill, but you can get a hose and run it downhill from the unit.

For Dehumidifier reviews, visit


"Great calculator you built!" -JoAnne, August 2013

"You are terrific. Thanks SO much for your information." -Alan, June 2013

Which Dehumidifier
Helping people find the right size dehumidifiers since 2008.
2608 Erwin Rd #148
Durham, NC 27705
(919) 383-1400

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