Air Purifier CADR Calculator

Enter the room size, ceiling height and what you are cleaning the air of. The page returns the CADR you need, the model tier that covers it, the noise to expect and how long the filter will last.

CADR is the clean air a purifier delivers per hour, and the number you need is set by the room, not by the marketing. Enter the floor area, ceiling height and what you are trying to remove; the page returns the CADR to aim for, the model tier that covers it, the noise to expect and a filter-life estimate.

The room

Area and ceiling height set the volume; the scenario sets how many air changes per hour the room needs.

Floor area (m²) Ceiling height What the room is like Main pollutant Hours run per day

CADR needed –

CADR to buy –

Covers up to –

Model tier –

Max noise (est.) –

Filter life (est.) –

How this was worked out

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Model tiers at a glance

CADR	Everyday	Allergy	Smoking	Max noise	Typical room
200 m³/h	14.3 ㎡	11.9 ㎡	8.9 ㎡	45 dB	Bedroom, study
300 m³/h	21.4 ㎡	17.9 ㎡	13.4 ㎡	51 dB	Small living room
400 m³/h	28.6 ㎡	23.8 ㎡	17.9 ㎡	56 dB	Living room
500 m³/h	35.7 ㎡	29.8 ㎡	22.3 ㎡	62 dB	Open-plan living
600 m³/h	42.9 ㎡	35.7 ㎡	26.8 ㎡	67 dB	Large living room
800 m³/h	57.1 ㎡	47.6 ㎡	35.7 ㎡	68 dB	Whole floor

Five rules that decide the purchase

CADR is measured in m³/h of clean air, so the target is room volume × air changes per hour — not floor area alone.
A 2.8 m ceiling is the usual assumption. A 3.2 m ceiling adds about 14% to the volume, and the CADR has to rise with it.
Buy 20% above the calculated figure. Filters lose airflow as they load, and a purifier at full speed is loud.
The three CADR figures on the box are for smoke, dust and pollen. Compare the one that matches your pollutant, not the biggest number.
CADR says nothing about filter life or gas removal. For formaldehyde and odours you also need the CCM figure and a carbon weight.

Practical notes

One purifier per floor works better than one large unit moved between rooms. Air does not travel through doorways on its own.
Keep the intake 20–30 cm off the wall and clear of curtains. A blocked intake can cut delivered CADR by a third.
Run it on high before bed and on sleep mode overnight. Noise is the reason most purifiers end up switched off.
Replace the HEPA when it turns grey or airflow drops, not only on the calendar. A loaded filter is quieter and cleaner-looking while doing less.

Four common mistakes

Sizing by floor area only. A 20 m² room with a 3.2 m ceiling needs 14% more CADR than the same room at 2.4 m.
Buying the biggest number on the box. A high CADR at 65 dB is unusable in a bedroom at night.
Expecting a particle filter to remove formaldehyde. HEPA catches particles; gases need activated carbon and a CCM rating.
Running it only when the air looks bad. PM2.5 is invisible, and the unit needs to run continuously to hold the level down.