Dehumidifier size calculator: Sample Methods to Calculate Dehumidifier Size and Capacity

Dehumidifier Size Calculator

Most of us face the problem of humidity at some point in life and using a dehumidifier is the best method to get rid of that problem. Dehumidifiers can prevent rooms from a musty smell and protect wallpaper, clothes, and other things. However, You must ask some questions to yourself before buying a dehumidifier. You should use a dehumidifier size calculator to know about the size of the dehumidifier you need. What will happen if you get a dehumidifier that is too big or too small? You will end up with either a huge electricity bill or a moist place.

Rooms of different sizes and different levels of humidity require different sizes of dehumidifiers. This is the reason why you should know about the size and capacity of the dehumidifier of your requirement. Calculating the size and capacity can be difficult if you don’t have the proper guide to do it. Wrong calculations will cause more trouble for you. Our dehumidifier size calculator and the guide on how to use it will make dehumidifier capacity calculation easier. There are various methods to calculate dehumidifier size, this guide will discuss some of the most effective methods. So, read till the end to learn how to calculate dehumidifier size and capacity.

Dehumidifier Size Calculator

The capacity or size calculation is the first step in choosing the most suitable dehumidifier. Instead of searching how much a particular dehumidifier can dehumidify, you can just use our dehumidifier size calculator. Our calculator is easy to use and gives accurate results.

To calculate the dehumidifier capacity using the above dehumidifier size calculator you need to fill in some details. An explanation of the parameters that you need to fill in the boxes is given below.

Present Temperature T (°C)

The first thing that you need to enter in the dehumidifier size calculator is the present temperature. You can easily check the temperature of your room, RV, bathroom, etc. with the help of a thermometer. Place the thermometer in the center of the place and it will provide you with a reading of the temperature. You should note that this will be according to your current room temperature. You can enter the highest recorded temperature to calculate the worst possible scenario. For example, if you face high humidity on rainy days, you can enter the highest temperature reading of a rainy day. This will prepare you for the moistest days but it will increase the size of the dehumidifier which means higher electricity bills. If the temperature at your place is less than 10°C, then it is better to use a desiccant dehumidifier or compressor dehumidifier with a de-icing feature.

Present relative humidity level (% RH)

While recording the humidity level of your place you need to consider your surroundings. Are you entering the humidity level of open space or closed space? If it is an open space like a warehouse you can easily get the readings from your local weather reports. However, in the case of a closed space like an office, room, or RV, you need accurate readings. You may use a hygrometer to get the actual ratings. Most hygrometers can also measure the temperature. You can use the same trick we used for “present temperature” to calculate dehumidification capacity for the most humid day.

Desired humidity (%RH)

In this column, you have to enter the humidity level that you want to achieve after installing a dehumidifier. Humidity levels should be different for different places. For example, the humidity level inside a walk-in freezer should be 60% to 65%. On the other hand, it should be 40% to 60% inside a room or office.

Room Volume (m3)

While using a dehumidifier size calculator, it is important to consider the proper room volume. The performance of a dehumidifier highly depends on the size of your room or RV or any area. If you have a dehumidifier that cannot handle the big size of your house, then your house will stay humid. To prevent that, calculate the room volume properly. It is very easy to calculate the value of a room or any enclosed space. The first thing you have to do is measure the length, width, and height in meters and then multiply them all. Enter the volume in the box and you will get the dehumidification capacity. If the area is very big, you might need to install multiple dehumidifiers to get rid of the humidity.  

Explanation The Results of Dehumidifier Size Calculator

The results tell you the size your dehumidifier should have under the conditions entered by you. To put it in simple words, this is the amount of water that your dehumidifier should be able to remove to achieve the desired humidity.

A dehumidifier’s capacity is the amount of water it can remove in a specific amount of time. For example, a dehumidifier with the capacity of 30 pints/day can remove 30 pints of moisture in a day. Our calculator provides you with results in “pints per day”. This means that the dehumidifier should remove this much amount of water from the air to achieve the desired humidity level. Now you know how to use our dehumidifier sizing calculator and what the results mean.

Dehumidifier Size Calculation Formula and How to Use It

In this section, you will learn about the formulas to calculate dehumidifier size.

Dehumidification Size (gram per hour) = (Present Absolute humidity – Desired Absolute humidity) × Room size

You can calculate the dehumidification size to select a suitable dehumidifier for residential, commercial, or industrial use by following the steps given below.

Step 1. The first step is to take all the measurements. The first thing that you need to measure is the present temperature and present relative humidity (%RH). Then, you have to decide the humidity level that you want to maintain in your room or any other place. The optimum humidity level for a normal place like a room or an RV is 40% to 60%. After that, we need the volume of the room. Measure the length, width, and height of the room and multiply those dimensions to get the volume.

Step 2. The second step is to convert the present humidity into absolute humidity. We can express the amount of water vapor that is present in the air as the percentage of the maximum amount of water vapor that air can hold at a specific temperature. On the other hand, absolute humidity is the amount of water vapor present in a given volume of air.

To calculate absolute humidity (AH) from relative humidity (RH) you can use the formula given below.

AH = RH × Mass of water vapor

Now you might be wondering about how to know the mass of water vapor in the air. You can use the following table to determine the mass of water vapor.

Temperature Mass of water vapor

Step 3. Convert desired humidity into absolute humidity using the same method used in step 2. You can also use an online absolute humidity converter.

Step 4. Subtract the result of step 3 from the result of step 2. The answer you get after subtracting the numbers is the volume of humidity that needs to be  removed per cubic meter.

Step 5. To find the required size of the dehumidifier, multiply the result of step 4 by the total volume of the room that we calculated in step one. So the formula to calculate the size of a dehumidifier is

Dehumidification Size (gram per hour) = (Present Absolute humidity – Desired Absolute humidity) × Room size

Multiplication factor for dehumidification size is 2.11337642. Multiply the answer from the above formula by 2.11337642 to derive pint per day from liter per day

Explanation of Dehumidifier Size Calculation Formula

It is easier to understand things with the help of examples. So, let’s take an example to understand the process of dehumidifier size calculation.

Let’s assume the following values:

  1. Present room temperature is 30°C.
  2. Present humidity level is 70% RH.
  3. Desired humidity level of the place is 40%.
  4. Dimensions of the place are 4 meters (L) x 5 meters (W) x 5 meters (H).

Dehumidifier size Calculation process:

Firstly, we have to calculate absolute humidity levels for both present and desired levels. We will get 21.25 grams/cubic meter for the present absolute humidity and 12.142 grams/cubic meter for the desired absolute humidity. And the volume of the room will be 4x5x5 which equals 100 cubic meters.

The difference between the values of absolute humidities is 9.108 grams per cubic meter. This means that the dehumidifier needs to remove 9.108 liters of moisture per cubic meter to achieve a level of 40% RH. which means that 100 cubic meters require a dehumidifier with a capacity of 910.8 grams (9.108 x 100) per hour.

910.8 grams per hour equals 0.9108 Kilograms per hour or  0.9108 liters per hour. If we calculate the value for a day, it will be 21.86 liters per day. So, you need a dehumidifier that has a capacity of 21.86 liters per day to meet your requirements.

The above results are in liters per day if you want to get the results in pints per day, all you have to do is multiply the above results by the dehumidification size multiplication factor of 2.11337642. So for the above example, you need a dehumidifier with a capacity of approximately 46.2 pints per day.

Calculate Dehumidifier Size by AHAM (Method 2)

There are many methods to calculate the size of the dehumidifier of your requirement. One of the most common methods is the dehumidifier size calculator by AHAM (Association of Home Appliance Manufacturers). It is a very simple method because you only have to read a chart and select the best-suited dehumidifier according to that chart. AHAM method might not be the most accurate method but this method is very efficient for home use. This method usually works on two factors. The level of humidity in that room or place is the first factor. The second factor is the size of the room and the size is measured in square feet. Let’s discuss both factors in detail.

Area classification according to the AHAM method

The first step towards selecting the right dehumidifier size through the AHAM method is to identify the type of area. All spaces do not have the same area and they also have different levels of humidity. So, there are mainly four types of spaces according to the AHAM method.

  1. Slightly Damp: A slightly damp space has a humidity level of 50-60%. This space could be your room, kitchen, RV, etc. The slightly damp area feels slightly heavy.
  2. Moderately damp: A moderately damp area has a humidity level of 60-70%. You will feel an uncomfortable environment and smell a musty odor occasionally.
  3. Very Damp:  We can see spots on the floor in very damp areas. A spot on the wall and a bad odor are also common symptoms of a very damp area. It has a humidity level of 70-80%.
  4. Wet: A wet area has a high humidity level of 80-100%. It is so high that condensation causes sweating on the wall. In the worst-case scenario, you may also observe seepage on the walls and floor.

Room measurements for dehumidifier sizing

The second step is to measure the size of the place where you wish to install the dehumidifier. Take the measurements of the room in which you want to install the dehumidifier. There is something that you should keep in mind while measuring the size of the place. If that place has a separate AC, then it is very simple, just measure the area. But if that AC works for two rooms then you need to consider the area of the other room also. In short, the total area covered by AC is an important factor. If you don’t consider that, you might get the wrong dehumidifier calculation. We will discuss the calculation of dehumidifier size with the AHAM method in the next section.

Dehumidifier Size Chart

Humidity Levels300
sq ft
sq ft
sq ft
sq ft
50-60% Humidity Slightly Damp
(Air feelsslightly heavy)
 20 pint 25-30 pint  35-40 pint 50 pint
60-70% Humidity Moderately damp
(Occasionalmusty smell)
 20 pint 25-30 pint 35-40 pint 50 pint
70-80% Humidity Very Damp
(Wet spotson walls or floor)
 25 pint 30 pint 45 pint 55 pint
80-100% Humidity Wet
(Seepage on walls, mold possible)
 25-30 pint 35-40 pint 45-50 pint 60 pint

It is very easy to understand the dehumidifier size chart and calculate the dehumidifier size. However, let’s take a look at some examples to understand the AHAM method more clearly.

Example 1 of Dehumidifier Size Calulation: Very Damp 500 Sq Ft Basement With RH of 80%.

The problem of a very damp basement is very common and many people face this issue. Basements typically have higher than average humidity, which can promote spore and mold growth. It can weaken the walls and jeopardize the entire structure of the house over time. Smart people get a dehumidifier to get rid of the humidity. You can also do that but you should carefully calculate the size of the dehumidifier. These are the values that we are going to consider for our example.

  • Area: 500 square feet
  • Relative humidity: 80%.
  • Average temperature: 21°C (approximately 70°F)

Now we have to check the table and see which dehumidifier is fit for our needs. You will notice in the table that a dehumidifier of 30 pints or 35-42 pint capacity is suitable to meet the above requirements. When you face a choice like this when you have to choose between a smaller and larger size dehumidifier, always go with the larger capacity. It is always preferable to have a more powerful dehumidifier than one that is insufficient for the job.

Keep in mind that the AHAM dehumidifier sizing chart does not account for average temperature. If you have a cold basement, increase the overall size of the dehumidifier by 10 pints. Dehumidifiers need to work extra hard in colder environments.

Example 2 of Dehumidifier Size Calulation: Moderately damp 1200 Sq Ft House With RH of 65%.

A single dehumidifier is enough for a house of small to average-sized house. Even though the house has more area than the basement, a house has less humidity than a basement. So, if you decide to install the correctly sized dehumidifier, you will not face the problem of humidity in your 1200 sq ft house. We will consider these values for this example.

  • Area: 1200 Square feet
  • Relative humidity: 65%.
  • Average temperature: 21°C (approximately 70°F)

After checking the dehumidifier size chart, it is easy to deduce that a house of 1200 sq ft and 65% relative humidity will need a dehumidifier with a capacity of 50 pints. This is how easy it is to use a dehumidifier size calculator or the chart and find a dehumidifier that suits your requirements.

Factors for Choose The Right Size Dehumidifier

There are a few things that you must keep in your mind while buying a dehumidifier of the right size.

Relative humidity rates

Relative humidity levels can range from 50% to 100% at a place. So, if a place has a high relative humidity rate, it means that it will require a dehumidifier of high power. If you end up buying a low-capacity dehumidifier at a place that has a relative humidity of 90%, the dehumidifier will be useless. Not only will it increase your electricity bill, but also it will not lower the humidity.

 Square footage

A smaller size dehumidifier can work and provide good results in a small place. However, if you install a low-capacity dehumidifier in a huge place, it will have no effect on the humidity. So, you should calculate the dehumidifier size properly before buying one.

Present temperature

Many people overlook this factor while selecting a dehumidifier for their basement, house, office, or RV. This is an important factor because the present temperature affects the performance of dehumidifiers. Refrigerant or compressor dehumidifiers work very well in normal and high temperatures. However, when the temperature is low, A dehumidifier needs to work harder than usual. If you are selecting a dehumidifier for a place that has a present temperature of less than 10°C, you should go for a desiccant dehumidifier at colder temperatures instead of a refrigerant dehumidifier.

Desired Humidity

Desired humidity is also an important factor that you must consider while choosing the size of your dehumidifier. If the relative humidity of the area is very high such as 90% and you want to bring it to 40%, It needs a high-capacity dehumidifier. On the other hand, if the desired humidity is only 10% less than the relative humidity, it will not require a high-capacity dehumidifier unless the area is very large.


Excessive moisture in a room or at any place can promote the growth of mold or mildew and even cause water damage. So, knowing that you need a dehumidifier is the first step. The second step is to determine the required capacity. The correct dehumidifier size calculation is very important to decide on the right size dehumidifier.

Now you know various methods that you can use to calculate dehumidifier size. You can use our dehumidifier size calculator which is the quickest way to find out the required capacity of your dehumidifier. You can also calculate the size with the help of the formula or the size chart. Choose the right dehumidifier now and control humidity at your fingertips.

Mohd Aqsat

Hi there, My name is Aqsat and I was born and raised in Delhi in India, and I have a degree in English from Amity University. I have acquired knowledge in various fields, such as education and e-learning, environment, health and care, finance, digital marketing etc. I have had the pleasure of working with a variety of home experts in my career. I have spent time helping these experts to build their businesses while assisting homeowners in caring for their greatest asset. I have been involved with indoor and vehicle air quality for a long time and feel that poor indoor air quality is one of the major problems. Now I have gotten the opportunity to share what I have learned. I hope you will find the content helpful.

Leave a Reply

Your email address will not be published. Required fields are marked *