Air Purifier Square Footage: How is it Calculated?

Calculating air purifier square footage is important in buying one for your home.

Air purifiers, after all, are incredible devices that improve the quality of life for many. 

They can remove particles from allergens, mold, and smoke from the air. This can improve the health of those living in the house and reduce the risk of asthma. 

To use an air purifier, you must first calculate the square footage of the room in which you want to use it. 

Then you need to find an air purifier that can circulate through that much space.

This article will teach you how to calculate air purifier square footage, what rating is needed to filter air effectively, and some of the health benefits associated with air purifiers.

How to Calculate the Room’s Square Footage

For most home appliances, you only need to calculate the square footage of the room’s floor. 

In this case, since an air purifier works with the total amount of air in a room, you need to calculate the volume of the room instead of the area.

You can do this by multiplying the width and length of the room by the height of the ceilings. 

The number you get from this will be the total volume of the room. 

You need to consider this number when looking at possible air purifiers

For example, say you have a room that is 8 feet long by 10 feet wide. This room also has an 8-foot ceiling. 

By multiplying all three numbers together, we get 640 feet.

This is the volume of the room in feet cubed, and that is the number you should have when comparing the capacity of air purifiers. 


How is Air Purifier Capacity Calculated?

Air purifier capacity is calculated considering the total speed of airflow in Air Changes per Hour or ACH. 

This number tells you how many times all the air in the room can be cycled through the purifier every hour. 

Generally speaking, you want a minimum of 2 ACH, more if you are dealing with allergies or other respiratory problems.

If an air purifier can cycle through 1500 feet cubed of air every hour, then it has a total room capacity of 750 cubic feet per hour. That way, it can cycle through the air twice.

Clean Air Delivery Rate

When you purchase an air purifier, you should look for one with a CADR or Clean Air Delivery Rate. 

This rating tells you how many cubic feet of air the air purifier can cycle through every hour.

If the model has a CADR rating of 200, it can cycle through 1,500 cubic feet of air space once every hour. 

By going to the Association of Home Appliance Manufacturers website, you will be able to see all the ratings and what square footage each rating correlates with. 

The bigger the room and the more ACH you want per hour, the higher of a rating you’ll want.

CADR Benefits

When calculating the CADR for an air purifier, the Association of Home Appliance Manufacturers considers both the airflow and the purifying efficiency of the machine. 

This makes it easier for consumers to decide which device to purchase because they can see how the machine’s features interact together.

It can be easy to pick a machine with a high airflow because it seems like it will get the room clean faster. 

However, that same machine could have low efficiency, which means that air isn’t getting as clean with every circulation.

The CADR allows you to consider both factors. 

That way, you can find the air purifier that offers maximum speed and quality for your home.

How to Calculate What Size Air Purifier You Need

All that information can get pretty confusing, especially when you’re looking at several different models that list their information in different ways. 

Fortunately, there’s a simple formula that you can use to calculate the CADR rating that you need in your next air purifier.

CADR Rating Formula

To calculate which CADR rating you need, you’ll need four numbers: the length, width, and height of your room, along with your desired ACH. 

Next, you’ll calculate the total volume of the room by multiplying the length, width, and height together. Then you’ll multiply that number by your desired ACH. 

Once all those numbers have been multiplied, you’ll want to divide that amount by 60. 

The resulting number is the CADR rating that you should look for in your next air purifier.


Here is an example of how to calculate your needed CADR rating. 

For this example, we are assuming the room is 20 x 20 x 8 and that we want an ACH of 2.

(L x W x H x ACH)/60

(20 x 20 x 8 x 2)/60

= 106

In this situation, we would need an air purifier with a minimum rating of 106.

CADR Chart

Room Square FootageSize at 2 ACHSize at 5 ACH
100 Sq Ft27 CFM67 CFM
150 Sq Ft40 CFM100 CFM
200 Sq Ft53 CFM133 CFM
250 Sq Ft67 CFM167 CFM
300 Sq Ft80 CFM200 CFM
350 Sq Ft93 CFM233 CFM
400 Sq Ft107 CFM267 CFM
450 Sq Ft120 CFM300 CFM
500 Sq Ft133 CFM333 CFM
600 Sq Ft160 CFM400 CFM
700 Sq Ft187 CFM467 CFM
800 Sq Ft213 CFM533 CFM
900 Sq Ft240 CFM600 CFM
1000 Sq Ft267 CFM667 CFM
1100 Sq Ft293 CFM733 CFM
1200 Sq Ft320 CFM800 CFM
1300 Sq Ft347 CFM867 CFM
1400 Sq Ft373 CFM933 CFM
1500 Sq Ft400 CFM1000 CFM
1600 Sq Ft427 CFM1067 CFM
1700 Sq Ft453 CFM1133 CFM
1800 Sq Ft480 CFM1200 CFM
1900 Sq Ft507 CFM1267 CFM
2000 Sq Ft533 CFM1333 CFM

Air Purifier Health Benefits

Using the previous section equation, you can figure out what rating you will need.

As long as you are using an air purifier that is appropriately rated, then there are significant health benefits associated with using an air purifier.

Air purifiers work to sterilize and filter the air. 

This can help people with health issues related to contaminants such as mold and pollen in the air. 

An air purifier can filter these particles out, which prevents them from causing irritation.

Air purifiers can also be an excellent choice for those that suffer from asthma. 

Asthma is often triggered by contaminants in the air, such as smoke or allergens, and can worsen with repeated exposure. 

Investing in an air purifier can help to reduce asthma symptoms by decreasing the triggering particles in the air.

Frequently Asked Questions

Here you will find the answers to some of the most frequently asked questions regarding air purifiers.

Does an air purifier work if the room is too big?

If the room is too big, your air purifier will still clean the air. 

However, an air purifier that is too small will not clean the air as efficiently as an appropriately sized air purifier.

To be effective, your air purifier must circulate through all the air in the room twice per hour. 

It will work as long as your air purifier is large enough to do this.

And don’t worry. There is no such thing as overcleaning the air when it comes to air purifiers. 

Your best bet is to purchase an air purifier larger than you anticipate needing.

That way, even if you expand later, your air purifier will be large enough to handle the extra space.

How big should my air purifier be?

Your air purifier should be large enough to circulate through all the air in the room twice per hour. 

If it is any smaller than this, it will not clean the air frequently enough to make a significant difference in air quality.

Is it better to have two smaller air purifiers or one big one?

With larger rooms, many people wonder if using one large air purifier is better than multiple filters. 

The answer to this question depends on the shape of our room.

Suppose the room is a large rectangle without any complex angles, and the air purifier can be placed toward the center of the room

In that case, a large air purifier should be adequate. 

If your room is complex and air does not flow well from one end to the other, it may be better to have multiple smaller air purifiers. 

That way, you can ensure that the current from the air purifiers is reaching every part of the room.

What size air purifier do I need for 1,000 square feet?

For a room of 1,000 square feet, you will need an air purifier with a CFM of at least 276 if you are basing your calculations on 2 ACH. 

If you want at least 5 ACH, you need at least 667 CFM to clean the air effectively. 

How do you measure air purifier effectiveness?

The primary metric used to measure air purifier effectiveness is the CADR, or Clean Air Delivery Rate, developed by the Association of Home Appliance Manufacturers. 

CADR measures how an air purifier can remove a target substance, usually dust, from the air. 

Based on the rate at which the purifier removes the contaminant, it will be assigned a number that correlates to a specific room size at different ACH.

Should air purifiers run 24 hours per day?

For maximum effectiveness, the air purifier should run for 24 hours a day. 

This allows the purifier to circulate the air through the room constantly and prevent contaminants from building up.

Keeping your air purifier on when you are asleep is especially important. Nighttime is one of the most common times asthma and allergy symptoms flare up. 

Keeping your air filter on at night will help prevent these symptoms from flaring up. 

If you turn your air purifier off at night, contaminants will build up in the air, which can cause an adverse reaction.


Key Takeaways

Air purifiers are fantastic devices that can help to improve the health of many by filtering allergens and other irritants out of the air. 

However, picking one rated with a CADR high enough for your home is essential for these devices to work. 

The CADR is a rating system that considers both the airflow and the cleaning efficiency of an air purifier

To determine which rating you need, you’ll need to multiply your room’s volume by the desired ACH, then divide that number by 60. 

You’ll want to pick a device that can filter your air at least twice per hour. 

If you are getting an air purifier to help with allergies or other respiratory problems, you’ll want to pick a machine with a higher rating.

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