How room size affects performance
A bigger room has more air volume, so it needs more CADR for the same number of air changes per hour. Ceiling height matters too because tall rooms contain more air than the floor area suggests.
Air Purifier Calculator for Cleaner Rooms.
Find the right CADR, HEPA filter level and purifier category for your room size, AQI and daily indoor conditions.
Your room needs approximately 4 complete air cleanings every hour.
At AQI 180, the air is unhealthy; keep windows closed during spikes.
Replace HEPA filters every 8-12 months, or sooner during heavy pollution seasons.
Higher CADR matters more than buying a purifier marketed for an oversized room.
What is CADR?
CADR tells you how quickly a purifier can clean room air.
CADR means Clean Air Delivery Rate. It estimates how much clean air a purifier can deliver per minute. For PM2.5 pollution, CADR is one of the most useful numbers because it connects purifier output to room volume.
A purifier with too little CADR may look good on paper but fail to clean a room fast enough during high AQI. A purifier with enough CADR can cycle the room air several times per hour, which is why this calculator focuses on ACH and room volume together.
Why AQI matters
Higher outdoor AQI usually means more particles entering through gaps, windows and doors. During very poor or hazardous AQI, higher ACH and closed-window operation become more important.
HEPA H13 vs H14
H13 is strong enough for most homes and Indian city PM2.5. H14 is a more medical-grade option, useful for highly sensitive users, clinics or severe pollution exposure.
FAQ
Common air purifier sizing questions
What CADR do I need?
CADR depends on room volume and the number of air changes per hour needed. A higher AQI, pets, smoking or asthma increases the required ACH and therefore the required CADR.
Can one purifier clean my whole house?
Usually no. Air purifiers work best in a defined room with closed doors and windows. Large homes usually need multiple purifiers placed in the rooms where people spend the most time.
Does a bigger purifier consume more electricity?
A higher-CADR purifier can use more power at maximum fan speed, but it may clean the room faster and run quieter at medium speed. Check the product power rating and noise level.
How often should I replace filters?
Most HEPA filters should be replaced every 8-12 months. In Indian winter pollution, heavy dust, pets or smoking environments, filters may need replacement sooner.
Is HEPA H13 enough for Indian cities?
HEPA H13 is a strong choice for PM2.5 in Indian cities. During severe AQI days or indoor smoke exposure, pair H13/H14 filtration with activated carbon and keep windows closed.