Air purifier sizing for a studio apartment

Researched from the AHAM AC-1 test method, EPA and CARB guidance, and published manufacturer specifications

Quick answer

A studio apartment is sized at 4.5 air changes an hour against a 9 foot ceiling on this site, so a 450 square foot one needs about 304 CFM of clean air delivery. The table below runs from 250 to 600 square feet.

Required CADR by floor area, 9 foot ceiling
Floor area	Volume	At 2 ACH	At 4.5 ACH	At 6 ACH
250 sq ft	2,250 cu ft	75 CFM	169 CFM	225 CFM
300 sq ft	2,700 cu ft	90 CFM	203 CFM	270 CFM
350 sq ft	3,150 cu ft	105 CFM	236 CFM	315 CFM
400 sq ft	3,600 cu ft	120 CFM	270 CFM	360 CFM
450 sq ft	4,050 cu ft	135 CFM	304 CFM	405 CFM
500 sq ft	4,500 cu ft	150 CFM	338 CFM	450 CFM
550 sq ft	4,950 cu ft	165 CFM	371 CFM	495 CFM
600 sq ft	5,400 cu ft	180 CFM	405 CFM	540 CFM

Meets 304 CFM, the extra large room class

WINIX 5510 Air Purifier (New Generation of 5500-2 with App Support) for Home Large Room Up to 1881 Ft2 in 1 Hr, True HEPA, High Deodorization Carbon Filter and Auto Mode, Captures Pet Allergies, Smoke

This machine can be credited with about 502 CFM, derived from the listing's own figures: 1881 sq ft at 2 air changes an hour, assuming an eight foot ceiling. That clears the 304 CFM this room calls for.

$179.99Check pricePrices change often

Check the noise at the speed that delivers the airflow, not the figure quoted for the lowest setting.

Every size in this room type

250 sq ft 169 CFM needed
300 sq ft 203 CFM needed
350 sq ft 236 CFM needed
400 sq ft 270 CFM needed
450 sq ft 304 CFM needed
500 sq ft 338 CFM needed
550 sq ft 371 CFM needed
600 sq ft 405 CFM needed

What makes a studio apartment different

The usual sources in this room are cooking particles, with no wall between the hob and the bed, dust, odour that has nowhere to go. That mix is what decides whether the carbon stage matters as much as the particle stage, and it is why the same square footage in two different rooms does not always call for the same machine.

In a studio the kitchen and the bedroom are the same room, so cooking particles reach the bed every time. If the extraction is a recirculating hood rather than a duct to the outside, it removes grease and very little else, and the purifier is doing more of the work than the label suggests.

Which air change target this room is sized at

This section sizes a studio apartment at 4.5 air changes an hour, the allergy and asthma households case, which suits pollen, pet dander or dust mite debris, where somebody in the house notices the difference. Two changes an hour is the comfort baseline and six is where smoke guidance sits.

The target is guidance rather than a measured threshold, so it is worth knowing what moving it does. Going from two changes an hour to 4.5 multiplies the airflow you need by 2.3, and the noise and the filter cost move with it.

Machines sized for this room

Each of these publishes either a CADR or a coverage claim with the air change rate behind it, so it can be compared against the requirement above.

MOOKA
MOOKA H13 HEPA Air Purifier for Home Pet Large Room Up to 1300ft2, Black
- HEPA claimed
- carbon stage
- has a UV lamp
$46.98 Check price
Prices change often
MOOKA
MOOKA Air Purifiers for Home Room up to 1076ft2, True HEPA Filter, B-D02L
- HEPA claimed
- carbon stage
$49.99 Check price
Prices change often
MOOKA
MOOKA Air Purifiers for Home Room up to 1076ft2, True HEPA Filter, B-D02L
- HEPA claimed
- carbon stage
$49.99 Check price
Prices change often
Afloia
Afloia Air Purifier for Large Rooms Up to 2,000 Sq. Ft. with PM2.5 Display
- carbon stage
- washable pre-filter
- particle sensor
- auto mode
$79.99 Check price
Prices change often
Winix
WINIX 5520 Air Purifier for Home Large Room Up to 1882 Ft2 in 1 Hr With Air Quality Monitor, True HEPA, High Deodorization Carbon Filter and Auto Mode, Captures Pet Allergies, Smoke, Dust.
- HEPA claimed
- particle sensor
- auto mode
- app or voice
$179.99 Check price
Prices change often
Instant
Instant HEPA Quiet Air Purifier From the Makers of Instant Pot with Plasma Ion Technology for Rooms up to 1140ft2, removes 99% of Dust, Smoke, Odors, Pollen & Pet Hair, for Bedrooms, Offices, Pearl
- carbon stage
- auto mode
- has an ionizer
$199.99 Check price
Prices change often

Common questions

What size purifier does a studio apartment need?

Multiply the floor area by the ceiling height, multiply by the air changes an hour you want, and divide by sixty. At 9 feet and 4.5 changes an hour, a 300 square foot studio apartment needs about 203 CFM and a 600 square foot one needs about 405 CFM.

Should I buy one large unit or two smaller ones?

Two smaller machines usually mix a room better than one large one, because a single unit recirculates its own clean air in the corner it sits in. One larger machine is quieter for the same total airflow and costs less to keep in filters. If the room is long or L shaped, two is the better answer more often than the arithmetic alone suggests.

Does the door being open change the sizing?

It does, and by more than people expect. An open door connects the room to a hallway and often to a stairwell, and the machine is then serving that whole volume rather than the room on the floor plan. Either size for the connected space or close the door during the hours that matter.

Is a higher air change rate always better?

No. Airflow costs noise, power and filter life, and past a point the room is already as clean as the filter can make it. The honest ceiling is the arrival rate of whatever you are removing: on a smoke day more is genuinely better, and on an ordinary day in an ordinary house it is not.

Do these figures assume anything about the filter?

They assume the machine delivers its rated clean air delivery rate, which a clogged filter does not. A filter at the end of its life moves less air at the same fan speed, so the effective air change rate drops quietly over months without the machine sounding any different.