Sizing

Read the room-size rating and CADR together

Room-size numbers are useful only when their air-change assumptions are clear. A rating at one air change per hour says the listed volume of air passes through the purifier once in an hour under the manufacturer's calculation. A 4.8-ACH rating represents a faster repeated turnover. The same purifier therefore gets a larger square-foot figure at one change per hour than at nearly five. Do not compare one model's one-change number with another model's faster-rate number as though they were equivalent.

Use one air-change basis across the shortlist

For these three Core models, Levoit publishes 1,051, 1,718 and 2,909 square feet at one ACH for the Core 300S-P, 400S-P and 600S-P. At 4.8 ACH, the corresponding figures are 219, 358 and 606 square feet. The second set is the relevant comparison if you want roughly repeated cleaning close to five room volumes per hour. It is still a manufacturer rating, not a guarantee of the air in a specific occupied room.

CADR—clean air delivery rate—offers another way to compare how quickly a purifier supplies cleaned air. The listed Core values are 141, 231 and 391 cubic feet per minute. In general, higher CADR supports a larger or faster-cleaned space, but it does not erase the need to check noise, fan setting, room geometry and placement. A purifier rated for 600 square feet at high speed will not deliver the same rate if you mostly run it at a quieter mode.

Include the air outside the tape measure

Square footage assumes a room boundary, while everyday homes have open doors, connecting spaces and high or vaulted ceilings. If a purifier sits in a living room that opens into a kitchen, decide whether the combined space is the job. A single unit can have trouble moving air around corners or through doorways, even if the combined floor area looks close to the product's label. Position the purifier in the space where air circulation is useful, keep it away from obstructions and preserve the manual's stated clearances.

Filters also change the usable flow. A clogged pre-filter or overdue main filter can restrict airflow. Treat the manufacturer's room figure as an apples-to-apples starting point, then consider the physical setup and your normal speed choice. For a room close to the threshold, leave a margin or choose a model with enough capacity that you can use a lower speed without falling below your intended turnover.

Don't interpret the rating as a health claim

A room-size label is an equipment sizing reference. It does not establish a medical benefit, guarantee that an allergen is eliminated, or show what is present in the air. A particle sensor may provide useful feedback about PM2.5, but it cannot identify every contaminant or tell you whether a pollutant source has stopped. Use a purifier alongside source control, ventilation and advice from the relevant safety authority when dealing with smoke, combustion or a specific chemical concern.

For model-specific context, compare the 219-square-foot Core 300S-P, 358-square-foot Core 400S-P and 606-square-foot Core 600S-P at the same 4.8-ACH rate. Then use the finder only for room and body requirements that are essential.