What Is CADR in Air Purifiers — and Why Does It Matter More Than Filter Grade?
In This Guide
- What Is CADR — and What Does the Number Mean?
- How to Calculate the Right CADR for Your Room
- Why Filter Grade Alone Is an Incomplete Buying Signal
- CADR vs Filter Grade — Which Should You Prioritise?
- Why 250 m³/h Is the Sweet Spot for Most Indian Rooms
- CADR by Room Type — Quick Reference for Indian Homes
- Key Takeaways
- Experience It
- Frequently Asked Questions
- Sources
In 2021, India's Bureau of Indian Standards published IS 17531:2021 — the national specification for portable electric indoor air purifiers — establishing performance requirements, CADR testing methodology, safety standards, and ozone emission limits for every purifier sold in the country. The reason this standard matters: too many products had been marketed on filter grade alone — HEPA H11, H12, H13 — while delivering real-world cleaning performance that fell far short of the label. CADR, or Clean Air Delivery Rate, is the number that tells you how fast a purifier actually cleans the air in your room. It is the single most useful specification to check before buying.
This guide explains what CADR means, how to use it to size an air purifier for any room, and why filter grade alone is an incomplete — and sometimes misleading — buying signal.
What Is CADR in Air Purifiers — and What Does the Number Mean?
CADR stands for Clean Air Delivery Rate. It measures the volume of clean, filtered air an air purifier produces per hour, expressed in cubic metres per hour (m³/h) or cubic feet per minute (cfm). A CADR of 250 m³/h means the purifier delivers 250 cubic metres of scrubbed, clean air every hour.
The metric was established by the Association of Home Appliance Manufacturers (AHAM) in the United States and has since become the global benchmark for comparing air purifiers across brands. India's BIS IS 17531:2021 standard incorporates equivalent testing requirements — making independently verified CADR figures part of the official specification framework for purifiers sold domestically.
CADR is measured across three particle size categories, each corresponding to a different class of common indoor pollutant:
| Particle Category | Size Range | Typical Source in Indian Homes |
|---|---|---|
| Smoke | 0.09 – 1.0 µm | Cooking fumes, incense, vehicle exhaust infiltration |
| Dust | 0.5 – 3 µm | Soil particles, skin cells, textile fibres |
| Pollen | 5 – 11 µm | Outdoor pollen entering through ventilation gaps |
A purifier with a CADR of 250 m³/h delivers 250 cubic metres of filtered air per hour. However, how effectively this translates into lower pollution levels depends on more than the purifier alone — it also depends on how air moves through the room. A purifier positioned in a corner with poor circulation may filter the same air repeatedly while the far end of the room stays relatively uncleaned. This is why airflow within the room matters alongside CADR.
How to Calculate the Right CADR for Your Room Size
The AHAM rule of thumb is:
Minimum CADR (cfm) = Room area (sq ft) × 0.67
Since most Indian purifiers now publish CADR in m³/h rather than cfm, the metric equivalent — using the standard four air changes per hour (ACH) baseline — is:
Minimum CADR (m³/h) = Room volume (m³) × 4
For a full framework on improving indoor air quality — beyond CADR — see our complete IAQ guide for Indian homes.
In cities with consistently high pollution — Delhi, Kanpur, Patna, Ahmedabad — a target of 5–6 ACH is more appropriate during summer and winter peak pollution months.
| Room Size | Ceiling Height | Air Volume | Min CADR (4 ACH) | Recommended (5 ACH) |
|---|---|---|---|---|
| 100 sq ft | 10 ft | 28 m³ | 112 m³/h | 140 m³/h |
| 150 sq ft | 10 ft | 42 m³ | 168 m³/h | 210 m³/h |
| 180 sq ft | 10 ft | 50 m³ | 200 m³/h | 250 m³/h |
| 200 sq ft | 10 ft | 56 m³ | 224 m³/h | 280 m³/h |
| 250 sq ft | 10 ft | 70 m³ | 280 m³/h | 350 m³/h |
These figures assume a well-mixed room with adequate air circulation. In rooms with stagnant air, open doors, or active sources of outdoor pollution entering through ventilation gaps, effective CADR is reduced. A slightly higher CADR or improved room circulation is advisable in these conditions.
Why Filter Grade Alone Is an Incomplete Buying Signal
Walk into any electronics showroom or product listing in India and the default sales pitch centres on HEPA grade — H11, H12, H13, occasionally H14. These grades describe a filter's particle capture efficiency at one specific particle size: 0.3 µm, known as the Most Penetrating Particle Size (MPPS). An H13 filter captures 99.95% of particles at 0.3 µm in a single pass. An H10 filter captures 85%.
What filter grade does not tell you is how fast that filter processes the air in your room.
Consider the analogy of a water tap. Filter grade is the quality of the filter cartridge on the tap. CADR is how fast water flows through it. A laboratory-grade filter on a tap that barely trickles still leaves you waiting a long time for clean water — and in the interim, you are still drinking from the contaminated supply.
An air purifier with an H13 filter and a weak motor may deliver a CADR of only 80–120 m³/h. In a 200 sq ft room, that achieves fewer than 2 air changes per hour — far below the recommended minimum of 4. In the same room, a well-engineered H10-grade unit delivering 250 m³/h achieves 4.5 ACH and processes the entire room air volume in approximately 13 minutes.
| Scenario | Filter Grade | CADR | Practical Result |
|---|---|---|---|
| High CADR, H10 filter | H10 | 250 m³/h | Rapid air processing; effective for PM2.5 in Indian homes |
| Low CADR, H13 filter | H13 | 90 m³/h | High per-pass efficiency; very slow room air processing |
| Balanced system | H10–H12 | 200–250 m³/h | Optimal real-world performance for Indian homes |
According to CPCB monitoring data, Delhi's annual average PM2.5 concentration ranges from 80–120 µg/m³ — 16 to 24 times the WHO's revised 2021 safe annual limit of 5 µg/m³. At these pollution levels, the speed at which air is processed — CADR — matters far more than achieving perfect capture efficiency in one slow pass.
CADR vs Filter Grade — Which Should You Prioritise?
The answer depends on the primary pollutant in your environment.
For PM2.5 and cooking fumes — the dominant pollutants in Indian urban air — CADR is the primary number to optimise. The speed of air processing determines how quickly pollutant concentrations fall.
For ultrafine particles below 0.1 µm (diesel exhaust by-products, some cooking gases) — filter grade matters more. Households near high-traffic roads should prioritise H10-grade or above alongside high CADR.
For allergens — pollen, dust, pet dander — both matter equally. The priority is high ACH to remove them quickly before they resettle.
Practical priority order for Indian buyers:
- CADR ≥ the minimum required for your room volume (× 4 ACH; × 5–6 for high-pollution cities)
- Filter grade H10 or above, BIS IS 17531:2021 certified
- Noise level — below 35 dB at low speed for bedroom use
- Filter replacement cost and annual availability in your city
- Smart features — app control, auto PM2.5 mode, scheduling
BIS IS 17531:2021 certification requires independently verified CADR claims. Look for the BIS mark before purchasing.
Why 250 m³/h Is the Sweet Spot for Most Indian Rooms
A CADR of 250 m³/h covers a 150–180 sq ft room at 5 ACH — the range that spans the majority of Indian bedrooms and compact living rooms. It is the minimum reasonable CADR for any room where occupants spend extended time, particularly during sleeping hours when the body is most vulnerable to PM2.5 exposure.
For rooms up to 200 sq ft, a 250 m³/h CADR delivers approximately 4.5 ACH — adequate for standard air quality days and sufficient during moderate pollution events.
One nuance worth noting: CADR figures are tested in a sealed, well-mixed room. In Indian homes where exhaust fans, split AC units in fresh-air mode, and kitchen openings regularly introduce outdoor air, effective CADR is reduced. A slightly higher CADR or more frequent filter maintenance is advisable in these conditions.
The Karban Airzone delivers a CADR of 250 m³/h through its H10 HEPA-class filter, combined with a built-in air circulator delivering 3,900 CMH of room airflow — actively drawing room air through the filter rather than relying on passive drift. More on how the integrated system works at the Knowledge Hub.
CADR by Room Type — Quick Reference for Indian Homes
| CADR Band | Suitable Room Size | Ideal Use Case |
|---|---|---|
| Under 150 m³/h | Up to 130 sq ft | Small bedrooms, study rooms, nurseries |
| 150 – 250 m³/h | 130 – 220 sq ft | Standard bedrooms, home offices |
| 250 – 350 m³/h | 220 – 310 sq ft | Living rooms, open dining areas |
| 350 – 500 m³/h | 310 – 440 sq ft | Large living rooms, open-plan kitchens |
| Above 500 m³/h | 440+ sq ft | Commercial spaces, large open halls |
For families in metro cities, the 250–350 m³/h band — combined with H10 or higher filtration and BIS IS 17531:2021 certification — covers most residential needs.
Key Takeaways
- CADR measures the volume of air a purifier processes per hour — the most useful single number for comparing air purifiers.
- Filter grade = capture efficiency per pass. CADR = how many passes per hour. For Indian homes, CADR is the primary real-world indicator.
- Formula: room volume (m³) × 4 for minimum CADR; × 5–6 in high-pollution cities like Delhi, Kanpur, or Mumbai.
- BIS IS 17531:2021 covers CADR testing, filter efficiency, ozone limits, and electrical safety. Always verify before purchasing.
- 250 m³/h suits most Indian bedrooms and compact living rooms up to 180–200 sq ft at 4–5 ACH.
- CADR figures assume a well-mixed room. A purifier paired with strong room airflow delivers meaningfully better real-world results.
- Ceiling-mounted placement delivers clean air into the breathing zone from the very first second — a floor unit can take up to an hour to reach breathing height.
- Filter performance degrades as it captures particles — replace on schedule, especially before peak-pollution months.
- Target below 35 dB at low speed for bedroom use.
- CADR does not cover ultrafine particles below 0.1 µm — combine high CADR with H10-or-better filtration for comprehensive coverage.
Experience It
The Karban Airzone is the only ceiling-mounted 3-in-1 appliance that combines a bladeless fan, H10 HEPA-class air purifier, and dimmable chandelier light in a single unit. With a CADR of 250 m³/h paired with a built-in air circulator delivering 3,900 CMH of room airflow, it actively draws room air through the filter. Available in Black and White. BIS Certified. Designed and manufactured in India. Starting from ₹14,999.
can you make it
Frequently Asked Questions
What does CADR mean in an air purifier?
CADR stands for Clean Air Delivery Rate. It measures how much air a purifier processes per hour, expressed in m³/h. A CADR of 250 m³/h means 250 cubic metres of air — scrubbed of smoke, dust, and pollen — is delivered every hour. It is the most reliable number for comparing purifier performance across brands.
Is a higher CADR always better?
Not automatically. A higher CADR processes a larger room faster, but an oversized unit in a small room will be noisier than necessary. Match CADR to your room volume: multiply room volume in m³ by 4 for the minimum, or by 5–6 for high-pollution cities.
What CADR do I need for a 150 sq ft bedroom in India?
For a 150 sq ft bedroom with a 10-foot ceiling, air volume is approximately 42 m³. At 4 ACH, the minimum CADR is 168 m³/h. For high-pollution cities targeting 5 ACH, aim for at least 210 m³/h.
Is CADR or HEPA grade more important for Indian homes?
For PM2.5 and cooking fumes — the dominant pollutants in Indian cities — CADR is more important. The ideal combination is H10-or-better filtration paired with a CADR matched to your room size.
What CADR is needed for a 200 sq ft living room?
For a 200 sq ft living room with a 10-foot ceiling, target a minimum CADR of 224 m³/h (4 ACH) and ideally 280 m³/h (5 ACH). A unit rated at 250 m³/h provides adequate coverage for normal to moderate pollution conditions.
Does CADR decrease over time as the filter loads up?
Yes. As the filter captures more particles, airflow resistance increases and CADR falls. In high-pollution Indian cities, filter performance can degrade within 3–6 months. Replace on schedule, particularly before summer dust season in April.
Is BIS IS 17531:2021 certification important when buying an air purifier?
Yes. BIS IS 17531:2021 covers CADR testing methodology, filter efficiency, ozone emission limits (≤50 ppb), and electrical safety. A BIS-certified CADR has been independently tested — uncertified figures are self-reported. Always look for the ISI mark.
Can a ceiling fan with a built-in air purifier match a standalone floor unit?
Yes — and it outperforms from the very first moment. A ceiling-mounted purifier throws clean, filtered air directly into the breathing zone immediately. A floor-standing unit can take up to an hour for cleaner air to reach breathing height in a still room.
What CADR is needed for an open-plan living and dining area?
For an open-plan area of 350–450 sq ft, target a CADR of 350–500 m³/h. Consider two units at opposite ends rather than one high-CADR unit for more even air distribution.
Why do some Indian brands advertise filter grade but not CADR?
Filter grade is easier to market — "HEPA H13" sounds definitive without requiring contextual comparison. CADR can be directly checked against your room volume. With BIS IS 17531:2021 now applicable, brands without verified CADR figures warrant scrutiny.
Sources
- Bureau of Indian Standards — IS 17531:2021 — standardsbis.bsbedge.com
- AHAM — CADR Testing Protocol — ahamverifide.org
- Wikipedia — Clean Air Delivery Rate — wikipedia.org
- Smart Air Filters — CADR Calculation Guide — smartairfilters.com
- Daikin India — CADR, ACH and Room Size Guide — daikinairpurifier.co.in
- WHO — Global Air Quality Guidelines, 2021 — who.int
- CPCB — National Air Quality Monitoring — cpcb.nic.in
- HouseFresh — CADR Calculator — housefresh.com
- IQAir — India PM2.5 Data — iqair.com
- ICMR-NIIRNCD — Indoor PM2.5 in Urban Indian Homes — pmc.ncbi.nlm.nih.gov
- Trane — What Is CADR? — trane.com
- Science Advances — PM2.5 Estimates in India — science.org
- Aerosol and Air Quality Research — Air Purifier Performance Under Varying Airflow — link.springer.com
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