What Is CADR in an Air Purifier? How to Pick the Right Size (India Guide)

If you have ever stood in front of a shelf of air purifiers wondering why the box says "covers 700 sq ft" while the product page says "CADR 250", you are asking the right question: what is CADR in an air purifier, and does it tell you more than the room-size claim? It does, and it is the number to look at first. This guide explains CADR in plain language, shows how to work out the CADR you need for your room, and explains why two purifiers with the same "coverage" can clean very differently.

What is CADR in an air purifier?

CADR stands for Clean Air Delivery Rate. It tells you how much clean air a purifier delivers per unit of time, measured in a test chamber. The Association of Home Appliance Manufacturers (AHAM), which runs the standard test, describes it as the cleaning rate of specific particles by the air cleaner, with the natural decay of particles in the room subtracted, so the purifier only gets credit for its own cleaning.

In simple terms: a purifier with a CADR of 300 m³/h cleans the equivalent of 300 cubic metres of air per hour, as far as the test particles are concerned. A higher number means the purifier removes particles faster and can serve a bigger room.

CADR is measured at the purifier's highest fan speed, so at lower speeds the real figure is lower, and so is the noise.

What do the three CADR numbers mean?

The AHAM test uses three kinds of particles, and the EPA's guide to home air cleaners explains how to read them:

• Tobacco smoke: very small particles, about 0.09 to 1 micron. This is the closest match to fine PM2.5 from traffic, stubble burning and cooking smoke.
• Dust: medium particles, about 0.5 to 3 microns.
• Pollen: large particles, about 0.5 to 11 microns.

For polluted Indian cities, the smoke CADR is the number that matters most, because PM2.5 is made of very small particles. The EPA advises choosing a high smoke CADR for fine particles. Many Indian listings quote one CADR without saying which test particle it refers to. When a listing does not say, treat the number as an upper bound.

CADR units: cfm and m³/h

You will see CADR in two units:

• cfm (cubic feet per minute), used in the United States.
• m³/h (cubic metres per hour), used by most Indian listings.

To convert: 1 cfm = 1.699 m³/h. So 100 cfm is about 170 m³/h. A Blueair listing that says 283 cfm for smoke is about 480 m³/h.

How to find the CADR you need for your room

The EPA's sizing chart gives the minimum CADR for rooms with 8-foot ceilings:

The easy rule from that chart: CADR in m³/h should be at least about 1.1 times your floor area in square feet. So a 250 sq ft room needs about 275 m³/h. Two notes:

1. Higher ceilings need more. The chart assumes 8-foot ceilings. For a 10-foot ceiling, add about 25%.
2. Open plans count in full. If your living room opens into the dining area, add the connected area.

If you live in a heavily polluted city, such as Delhi NCR in winter, give yourself a margin, because indoor air is constantly being refreshed from outside every time a door opens. This margin is our own suggestion, not part of the EPA chart: we would add 20 to 30%.

Worked examples

• A 12 ft x 12 ft bedroom (144 sq ft, 10 ft ceiling): 144 x 1.1 x 1.25 = about 200 m³/h. A purifier with a CADR of 230 to 250 m³/h, such as the Philips AC0950 or the Mijia 4 Compact, is comfortable.
• A 15 ft x 18 ft living room (270 sq ft, 10 ft ceiling): 270 x 1.1 x 1.25 = about 370 m³/h. Look at 400 m³/h or more: the Cuckoo Respure (408) or Qubo Q600 (450).
• A 20 ft x 25 ft hall (500 sq ft, 10 ft ceiling): about 690 m³/h. No single purifier under ₹15,000 reaches this, so use two purifiers or move to a larger model.

CADR vs coverage claims

Room-size claims such as "covers 700 sq ft" or "purifies 1,076 sq ft" depend on how many times per hour the maker assumes the air is cleaned (air changes per hour, or ACH). The Dreo listings, for example, state their coverage "at 1 ACH", while Honeywell's V1 states 235 sq ft "with 2 air changes per hour". Philips lists two figures for its AC0950: 700 sq ft on one test basis and 320 sq ft on the stricter GB/T basis.

Because the assumptions differ, you cannot compare coverage figures between brands. CADR is measured the same way for every purifier, so it is the fair comparison. AHAM itself points out that ACH is a measure of ventilation, not of how much clean air a portable unit delivers.

A quick check you can do on any listing: divide the claimed coverage in sq ft by the CADR in m³/h. If the answer is near 1, the claim is conservative. If it is two or three, the maker assumed very few air changes and the claim will not hold in a polluted city.

CADR vs airflow

Do not confuse CADR with airflow. Airflow measures how much air the fan moves. CADR measures how much of that air comes out clean. Dyson, for example, publishes airflow in litres per second (over 290 L/s) and not a CADR, so you cannot compare a Dyson with a Coway on that figure alone.

CADR is not everything

CADR is the best single number, but it has limits. The EPA and AHAM both note:

• CADR covers particles only. There is no widely accepted rating for gas or odour removal, so a purifier with a high CADR may still do little for cooking smells or formaldehyde. Look for a substantial activated carbon layer.
• It does not test viruses or bacteria. AHAM makes no claims about them.
• Real rooms are harder. Air leaks, deposition on surfaces and doors opening mean a purifier may not reach its rated CADR in every room.
• Filters matter over time. A clogged filter reduces airflow, so check the filter life and replacement cost. See our Philips filter guide for a real example.

Also avoid ionizer and ozone-producing models. The EPA warns that ionizers, some UV devices and plasma cleaners may emit ozone, which irritates the lungs.

CADR of popular purifiers in India

These figures come from Amazon.in listings or the makers' pages, checked on 11 Nov 2026.

Many of these are manufacturer or listing claims, and few Indian listings state the test method. Use them to compare, not as a guarantee.

What to do with this

1. Measure your room and work out the CADR you need.
2. Choose a purifier with at least that CADR on the listing, and a filter you can replace affordably.
3. Check noise: a high CADR at full speed is loud, so you will probably run the purifier at a lower speed, which means a lower CADR in practice.

For specific picks, see our best air purifier under 10000, best air purifier under 15000 and best air purifier for Delhi NCR guides. If you are weighing brands, start with Qubo vs Coway vs Philips.

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