When shopping for a portable air purifier or air cleaner, one of the most important specifications to consider is the Clean Air Delivery Rate (CADR) rating. This rating plays a vital role in determining how well a purifier will perform in your home or office environment. But what exactly does CADR mean, and how is it calculated?
What Is CADR?
CADR stands for Clean Air Delivery Rate. It is a standardized metric developed by the Association of Home Appliance Manufacturers (AHAM) to measure the effectiveness of portable air purifiers. CADR indicates the volume of clean air (free from specific pollutants) that an air purifier can deliver per minute.
The CADR rating helps consumers compare the performance of different air purifiers in removing three main types of indoor air pollutants:
- Smoke (smallest particles, ~0.09–1.0 microns)
- Dust (medium particles, ~0.5–3 microns)
- Pollen (largest particles, ~5–11 microns)
Each type of particle has its own CADR score, usually ranging from 0 to 450 (depending on the unit’s size and power).
Air Purifier Sizing Chart
This Air Purifier or Air Cleaner sizing chart is based off the metrics used by AHAM in calculating the CADR values. The CADR values are based on 5 air changers per hour (ACH) and an 8 foot ceiling. The chart has two major columns, one based on Air Changes per Hour and the other based on ceiling height. If you don’t understand what air changes are then see our video on How to Calculate Air Changes per Hour.
If you know the square footage or square meters of the room you want to put the portable air purifier then find the room size in the first two columns and then move horizontally across until you reach the 5 Air Changes per Hour Column to get the CFM or the CADR rating for Smoke. There are three ratings found on air purifiers, but if you use the smoke value given on the Air Purifier then this will give you the best option for air flow. You can download a copy of this chart below.
Download this Air Purifier Sizing Chart
Ceiling Heights Greater than 8 Feet (2.4m)
If the room where you want to put the air purifier has a ceiling higher than 8 feet (2.4m), then you can use the blue columns. The adjustment for ceiling height uses the 5 air changes per hour value, so if you want more than 5 air changes per hour pick a size greater than what is shown in the table.
Clean Air Delivery Rate (CADR) Formula
The formula for calculating the Clean Air Delivery Rate (CADR) is very basic and takes into consideration everything in our chart above.
CADR = Room Area x Ceiling Height x Air Changes per Hour / 60 minutes in an Hour
What Does the CADR Rating Mean?
Let’s say an air purifier has the following CADR ratings:
- Smoke: 200
- Dust: 220
- Pollen: 250
This means the unit can reduce the concentration of smoke particles by delivering 200 cubic feet per minute (CFM) of clean air. The higher the number, the more efficient the unit is at cleaning the air for that particular particle type.
CADR ratings make it easier to choose an air purifier suited to the size of your room and the specific pollutants you’re targeting.
How Is CADR Calculated?
CADR is determined through controlled lab testing under AHAM standards. Here’s an overview of the process:
- Controlled Environment: The purifier is placed in a sealed chamber, typically around 1,008 cubic feet in volume.
- Pollutant Introduction: A measured amount of smoke, dust, or pollen is introduced into the air.
- Air Purifier Activation: The purifier runs at its highest fan speed.
- Measurement: Instruments track how quickly and effectively the unit reduces the concentration of each pollutant.
- Calculation: The CADR is calculated based on how fast the concentration of pollutants drops, factoring in natural air loss (decay) and the volume of the room.
The formula used by AHAM essentially looks at the rate of particle removal by the purifier minus the rate of natural decay, converted into a volume per minute.
Matching CADR to Room Size
AHAM recommends choosing a purifier with a CADR rating that is at least two-thirds the size of your room in square feet. For example:
- A 150 square foot room would need a purifier with a minimum CADR of 100.
- For larger rooms (like 300 sq ft), look for purifiers with CADRs of 200 or more.
Why Clean Air Deliver Rate (CADR) Matters
CADR is one of the few standardized, third-party tested metrics in the air purifier industry. It ensures:
- Objective performance comparisons
- Clarity in marketing claims
- Proper sizing of purifiers for effective cleaning
However, CADR has limitations. It doesn’t measure performance against gases, volatile organic compounds (VOCs), or microbes. It’s also based on short-term performance and does not account for noise level, filter lifespan, or energy use.
Final Thoughts
CADR is a critical number to understand when selecting a portable air purifier. It tells you how well a unit will remove common indoor pollutants like smoke, dust, and pollen. By understanding CADR ratings and how they’re calculated, you can confidently choose an air cleaner that meets the needs of your space and improves your indoor air quality.
If you’re trying to breathe cleaner air, don’t just go by brand name or fancy features — check the CADR ratings to make an informed choice.
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