Air Purifier Size Calculator
Calculate the recommended air purifier CADR (Clean Air Delivery Rate) for a room from its length, width, and ceiling height.
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ft
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1.5 ≈ 4-5 air changes per hour; increase for allergy-sensitive spaces
Recommended CADR
270
Room Area
180 sq ft
Room Volume
1440 cu ft
How Air Purifier Size Is Calculated
CADR (Clean Air Delivery Rate) measures how many cubic feet of filtered air a purifier delivers per minute — it's the standard spec manufacturers use to indicate how effectively a unit cleans air in a given room size. To pick a properly sized purifier, match its CADR rating to your room's size at a target air changes per hour (ACH), the number of times the purifier fully cycles the room's air each hour. A common guideline for typical living spaces is to aim for 4-5 ACH, which works out to roughly room area × 1.5 as an approximate recommended CADR — a simplified rule of thumb you can adjust based on your own target ACH or room use (bedrooms and allergy-sensitive spaces often want a higher multiplier).
Recommended CADR ≈ Room Area × Factor (default 1.5, for ~4-5 ACH)
Example
A 15 × 12 ft room has an area of 180 sq ft. Using the default factor of 1.5, the recommended CADR is about 270 — meaning you'd want to look for an air purifier rated at roughly 270 CADR or higher to adequately clean that room's air.
Common Use Cases
- Choosing the right size air purifier before buying one for a bedroom, living room, or office.
- Checking whether an existing purifier is actually rated for the room it's placed in.
- Comparing purifier models by matching their CADR rating to your specific room size.
FAQs
What is CADR, exactly?
CADR (Clean Air Delivery Rate) is an independently tested rating showing how much filtered air (in cubic feet per minute) a purifier delivers for smoke, dust, and pollen specifically. It's printed on most reputable air purifiers and is the standard way to compare cleaning power across models.
Why does ceiling height matter if it's not in the main formula?
This calculator's area-based estimate assumes a standard ceiling height (around 8 ft). Room volume is shown separately for reference — for unusually tall or vaulted ceilings, you may want to increase the recommended CADR factor since there's more total air volume to clean.
Should allergy sufferers use a higher CADR target?
Yes — people with allergies, asthma, or pet sensitivities often benefit from a higher air-changes-per-hour target (5 or more), which means increasing the factor input above the default 1.5 to get a higher recommended CADR.