Air purifier CADR is the number to check first when you shop, and it is the one most buyers skip. It tells you how quickly a unit can clean the air in a room. With winter smog returning in many cities, this guide shows how to match the rating to your room size.
Quick answer
- CADR means Clean Air Delivery Rate, the speed at which a purifier cleans a room’s air.
- Aim for 4 to 5 full air changes per hour.
- Needed CADR in m³/h is roughly room volume in m³ times air changes per hour.
- Look for true HEPA, a PM2.5 sensor and low noise on sleep mode.
- Budget ₹1,500 to ₹6,000 a year for filters.
What air purifier CADR actually measures
CADR is the volume of filtered air a purifier delivers over a set time. Eureka Forbes explains that the standard was developed by AHAM to compare units fairly. Each purifier lists separate ratings for dust, pollen and smoke, plus PM2.5.
Units differ by region. The US uses CFM, while Asia uses m³/h. Also, 1 CFM equals 1.69 m³/h, so convert before you compare two brands.
How to match CADR to your room size
The method is simple arithmetic. The same Eureka Forbes guide recommends 4 to 5 air changes per hour for most homes. So work through these steps:
- Multiply length by width by height to get the room volume.
- Multiply that volume by the air changes you want per hour.
- The result is the CADR you need, in m³/h if you used metres.
For example, a bedroom of 4 m by 3.5 m with a 2.8 m ceiling has a volume of 39.2 m³. At 5 air changes per hour, you need about 196 m³/h. So a unit rated near 200 m³/h or higher is a fair fit. This is our own calculation from that guidance, not a manufacturer rule.
Rules of thumb vary. Digit suggests at least 200 m³/h for a 300 sq ft bedroom, for instance. However, going slightly above the minimum suits Indian pollution levels. Avoid oversizing too much, because bigger units cost more and can be noisier.
Other specs worth checking
Match the unit to your city as well. Digit notes that Delhi NCR often sees AQI above 400, which calls for a higher CADR and thicker filters. Cities such as Hyderabad and Pune usually stay in the moderate range, where a mid range unit may do.
- True HEPA: it captures 99.97% of particles down to 0.3 microns. Be wary of “HEPA like” or “HEPA type” labels.
- PM2.5 sensor: it adjusts fan speed to the air quality in real time.
- Noise: look for under 50 dB on high and under 35 dB on sleep mode.
- Room coverage: a rated 200 sq ft unit will struggle in a 400 sq ft room.
What it costs to run
Filters need replacing every 6 to 12 months. Original filters cost ₹1,500 to ₹6,000, so yearly running costs can reach about ₹6,000. Check whether compatible third party filters exist and how long they last. Also, factor in electricity, since a unit that runs all night adds up.
Mistakes to avoid
The first mistake is buying on coverage area alone, since makers measure it differently. The second is placing the unit in a corner behind furniture. Then there is the habit of leaving doors open, which lets pollution back in faster than the unit can clean it.
For other home buying decisions, see our guides on reading the BEE star label on a geyser and checking an ISI mark with the BIS Care app. Both help you judge appliances before you pay.
FAQ
What is a good CADR for an air purifier in India?
It depends on your room. Multiply room volume in m³ by 4 to 5 air changes per hour to get the target in m³/h. For a typical 300 sq ft bedroom, Digit suggests at least 200 m³/h.
Is HEPA necessary in an air purifier?
A true HEPA filter captures 99.97% of particles down to 0.3 microns. Labels such as “HEPA type” may not meet that standard, so check the specification.
How often do air purifier filters need changing?
Usually every 6 to 12 months. Original filters cost about ₹1,500 to ₹6,000, so plan for yearly running costs.