What Size Dehumidifier Do I Need?

Dehumidifiers can make an incredible difference to the quality of air in your home, helping to reduce damp and mold as well as helping with all sorts of health conditions from asthma to allergies. Dehumidifiers come in a wide range of sizes and designs, however, and choosing the right one for your home can be confusing and difficult, particularly when it comes to finding the right size of dehumidifier for a room.

We at Best of Machinery are here to help, though. Below, we’ve broken down some of the most important features of dehumidifiers to help you understand how they work and what size you need for various sizes and types of room. This will help you to understand what size dehumidifier you need, making it easier to buy the right dehumidifier for your home and needs with ease.

Why do I Need a Dehumidifier?

Excessive moisture levels in the air can cause major problems to your home and your health. Damp air can lead to mold, condensation, and even structural damage to your walls, as well as unsightly staining, peeling wallpaper, and bad smells. It can also pose health risks, exacerbating allergies and conditions such as asthma and causing breathing difficulties.

A dehumidifier functions by sucking in air from its surroundings, pulling the water from it, and releasing the air again while the water is stored in the dehumidifier’s water tank. This cuts down the level of moisture that’s free to float around in the air, helping to dry out your living space and keep your living environment pleasant and well maintained. You’re looking for an ambient humidity level of 40% to 60%; if you use a dehumidifier that’s too small, it’ll struggle to keep the humidity down that low, and you’ll still suffer several of the health risks and negative effects of excess air moisture.

Size vs. Capacity

When you’re trying to work out what size dehumidifier you need to keep your room dry and comfortable, what you’re actually looking for is its capacity. Capacity refers to the amount of water a dehumidifier can extract from the air in a 24 hour period, rather than the physical size of the unit or its water storage tank; this is the most important way to measure the power and effect of a dehumidifier on a room, so it’s the metric most commonly used to compare dehumidifiers.

Most dehumidifiers very rarely reach their official capacity, as this number is the measure of peak performance in ideal conditions, a situation which most dehumidifiers will never actually experience. The rate of water extraction depends on several things, primarily the temperature and humidity of the surrounding air.

Working out the Size of your Room

The first thing you’re going to need to do is to work out how large the room you’re trying to dehumidify is. This can be easily achieved, as all you need is an approximate measurement; don’t worry too much about things like alcoves or oddly shaped corners. Simply measure the length and width of the room, and multiply them together to get the area of your room. This measurement, in square feet, is the most commonly used system for understanding room sizes and therefore appropriate dehumidifier capacity.

What Size Dehumidifier?

As a general guideline, for moderately damp conditions, the following sizes of dehumidifier are recommended. For wetter environments, simply pick the next size of dehumidifier up that’s available! For small rooms of up to 400 square feet: a dehumidifier with a 10-pint capacity should be plenty. Medium rooms of up to 800 square feet are suited for dehumidifiers with a capacity of approximately 1 gallon.

Larger rooms of approximately 1500 square feet need a dehumidifier with a daily capacity of approximately 2 gallons. Anything larger than this is going to prove a problem for most commercially available household dehumidifiers, and you’ll want to consider purchasing a whole house dehumidifier for rooms of that large a size.

Whole House Dehumidifiers

Whole house dehumidifiers are large and expensive dehumidifier units that can be either installed as standalone appliances or attached to a pre-existing central heating or air conditioning system. These devices present a major initial investment, but work efficiently enough that they can save you a large sum of money in the long term! If you’re trying to keep your entire house dry, or a single room with an area of over 1500 square feet, this is the best option, as whole house dehumidifiers are designed for spaces as large as 3000 square feet.


Dehumidifiers are an important piece of household equipment for anyone that lives in a more humid environment, and they can offer major benefits to both your health and the safety and cleanliness of your home. Buying the right size of dehumidifier is important, as the wrong size can fail to effectively dry out your living environment. With our guide above, hopefully, you’ll be better equipped to purchase the right size of dehumidifier for any room, understanding how and why you need specific sizes for different spaces and conditions.

With Best of Machinery guides, you can buy with full confidence that you’re making a good decision and finding the perfect dehumidifier for your home, no matter what size of house you live in or how high the ambient moisture level may be.

About the Author

Bob Robinson has been a tool enthusiast and lawn care expert for the past 11 years. First working with John Deere to reduce their impact on the environment, whilst building his love for writing in his spare time. Now, Bob runs the editorial team at BestofMachinery and tends to his garden in his spare time.

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