Walk into any electronics showroom in India and you will hear a lot of confident numbers — “five-stage filtration”, “captures 99.97% of particles”, “ioniser plus UV”. Most of them tell you almost nothing about whether the machine will actually clean your room. The one number that does is usually printed small, sometimes left off the box entirely: CADR.
CADR is short for Clean Air Delivery Rate. In one figure it answers the only question that matters when you are buying — how much clean air does this purifier actually push out per hour? A high-grade HEPA filter that sits inside a weak fan is like a brilliant water filter attached to a dripping tap: the filtration is real, but barely any treated air reaches the room. CADR measures the whole machine working together, not just the filter on its own.
This guide explains the CADR meaning for an air purifier in plain language, then shows you how to match it to your room size — a 12×12 Mumbai bedroom, an open Gurugram living-dining, a child’s nursery in Bengaluru. Get this one number right and almost every other buying decision becomes easier. Get it wrong and you will own a purifier that hums away all day while the air barely changes.
What CADR actually means
CADR is the volume of clean, filtered air a purifier delivers in a fixed time, usually stated in cubic metres per hour (m³/hr) in India, or cubic feet per minute (CFM) on imported boxes. A purifier rated at 300 m³/hr is, in effect, producing 300 cubic metres of genuinely filtered air every hour on its highest tested speed.
Two machines can carry the exact same HEPA filter and post wildly different CADR numbers. The difference is the fan, the seal around the filter, and how the air is routed. A loose seal lets dirty air slip past the filter — “bypass” — and that leaked air still leaves the machine, just uncleaned. CADR quietly punishes all of this. That is why it is a fairer measure than filter grade alone.
You will sometimes see separate CADR figures for smoke, dust and pollen, because particles of different sizes are captured at slightly different rates. For Indian conditions — where fine PM2.5 from traffic, crop burning and construction is the main worry — the smoke CADR is the most honest one to compare, since it is measured against the smallest, hardest-to-catch particles.
CADR is not the same as coverage area
Brands love to advertise “coverage up to 500 sq ft”. Treat that figure with care. Coverage is a marketing-friendly translation of CADR, and the assumptions behind it vary from brand to brand. Some quote coverage at one air change per hour — barely a trickle — which inflates the square-footage claim. The honest standard, set by the body that defines CADR testing, assumes a brisker turnover. Always trace coverage back to the raw CADR number if you can.
The CADR rule of thumb for Indian rooms
Here is the practical version you can use in a shop. A trustworthy purifier should be able to clean the air in your room roughly four to five times every hour. Air-quality people call this ACH — air changes per hour. Five ACH means the entire volume of air in the room passes through the filter five times in sixty minutes, which is what you want when the city outside is having a bad day.
The arithmetic is simpler than it looks:
- Work out your room’s floor area in square feet (length × width).
- Multiply by the ceiling height to get volume. Most Indian flats have ceilings around 10 ft.
- For 5 ACH, you want a CADR of at least (room volume in m³ × 5).
If you prefer to skip the maths, a reliable shortcut for a standard 10 ft ceiling is: your room’s area in square feet, multiplied by about 1.5, gives the minimum CADR in m³/hr you should look for. A 150 sq ft bedroom wants roughly 225 m³/hr. A 300 sq ft living room wants around 450 m³/hr. It is a rough guide, but it keeps you honest and stops you from buying a machine that is hopelessly underpowered for the space.
A room-by-room table for typical Indian homes
| Room | Typical size | Floor area | Minimum CADR (≈5 ACH) |
|---|---|---|---|
| Child’s room / small bedroom | 10×10 ft | 100 sq ft | ~150 m³/hr |
| Master bedroom | 12×12 ft | 144 sq ft | ~220 m³/hr |
| Large bedroom | 12×15 ft | 180 sq ft | ~270 m³/hr |
| Living room | 15×18 ft | 270 sq ft | ~400 m³/hr |
| Open living-dining | 18×24 ft | 432 sq ft | ~650 m³/hr |
These are floors, not targets. If your city’s air is regularly severe, aim higher — and we will get to why in a moment.
Why you should size up, not down
When a room sits between two purifier models, the instinct is to save a little money and pick the smaller one. Resist it. A purifier with CADR to spare runs on a lower fan speed to do the same job. Lower speed means it is quieter at night, it sips less electricity, and the filter lasts longer because less air is being forced through it per hour. You get the same clean air for less noise and a smaller running cost.
An undersized purifier does the opposite. It runs flat out on turbo all day, roaring next to your bed, burning more units on your electricity bill, and still falling behind on a smoky winter evening. The fan and filter wear faster. It is the worst of every world. Buying slightly bigger than you think you need is almost always the smarter rupee.
There is a real-world catch, too. Manufacturers measure CADR in a sealed test chamber with the purifier on its loudest speed. At home, your door opens, the window has a gap, and you will probably run it on a quieter medium speed overnight. Real delivered clean air is usually a good bit lower than the lab number. Headroom absorbs that gap.
CADR and your city’s air
The 5 ACH rule of thumb is a sensible baseline. But baselines assume average days, and large parts of India do not get average days for months at a time. Delhi’s winter AQI routinely crosses 300, and during crop-burning weeks it climbs far past that. When the air coming in under your door is that dirty, the purifier has to work much harder just to hold the line.
So treat your room as a little larger than its floor area if you live somewhere with punishing seasonal air — Delhi-NCR, parts of the Indo-Gangetic plain, or any city downwind of heavy construction. Push your target from 5 ACH toward 6 or even 8. Practically, that means buying a purifier whose CADR comfortably clears the table above. Our air purifier guide for Delhi pollution walks through exactly how much extra headroom a severe-AQI city deserves.
Milder cities can stick closer to the baseline. A coastal home in Chennai or a leafy Bengaluru neighbourhood will not see Delhi’s winter numbers, so you can size to the standard rule without much penalty. Be honest about your own street, though — proximity to a main road, a construction site, or open burning can make a “clean” city’s microclimate surprisingly bad.
One thing CADR cannot do, however good the number: it cannot fix the air outside your walls. A purifier cleans the air in one room. It does not turn your flat into a sealed bubble, and it does not improve the city. On a high-AQI day it is a tool to make your indoor air markedly better than the outdoor air — not a cure for the season.
Where CADR ends and filtration begins
CADR tells you about quantity — how much air gets cleaned. It says far less about what gets cleaned out of it. That is where the filter type matters, and the two numbers work as a pair.
A true HEPA filter is the part that captures the fine particulates. The H13 standard, for instance, is defined as capturing 99.95% of particles at 0.3 microns — the size that is hardest to trap. An activated-carbon stage is what tackles odours and gases: kitchen smells, the sharp note of fresh paint, vehicle fumes that drift in. CADR mostly reflects the particle side; it does not capture how well the carbon handles smell. If odour and gases matter to you, look for a genuine carbon layer with real weight to it, not a thin cosmetic mesh.
This is also why you should be wary of ionisers sold as a CADR shortcut. Some machines inflate their effective clean-air claim with an ioniser that charges particles so they stick to surfaces — they leave the air, but they land on your floor and walls rather than being trapped in a filter, and some designs can produce trace ozone. We unpack the trade-offs in HEPA vs ioniser vs activated carbon. The short version: for Indian indoor air, mechanical HEPA filtration with a solid CADR is the dependable choice.
[gnr_img name=”diagram-hepa-stages” alt=”Cutaway diagram of an air purifier showing pre-filter, activated carbon and HEPA stages with airflow” w=”1200″ h=”800″]
Reading a spec sheet without getting fooled
Now that you know what CADR means, here is how to use it when a spec sheet is in front of you, whether in a showroom in Pune or a product page at 1 a.m.
- Find the raw CADR in m³/hr or CFM. If the listing only shows “coverage area” and no CADR at all, that is a small red flag. Ask, or look it up.
- Check the speed it was measured on. CADR is quoted on turbo. Make sure the noise level on that same speed is liveable — a purifier you mute at night is not cleaning at its rated CADR.
- Convert CFM to m³/hr if needed. Multiply CFM by about 1.7 to get m³/hr. A 200 CFM machine is roughly 340 m³/hr.
- Match it to your room with the table above, then add headroom for your city.
- Factor in running cost, not just the sticker. Filters are a recurring spend and electricity adds up over a year. A bigger machine running on low usually costs less to run than a small one stuck on turbo, GST included.
For Girnaar’s own purifiers, you will find the exact CADR and tested coverage on each product page rather than in this article — our CADR figures are [SPEC_PLACEHOLDER] and we would rather you read them straight from the spec than from a blog. The buying logic, though, is the same one above.
Putting it together
CADR is the honest headline number. Measure your room, apply the rough rule — area in square feet times about 1.5 for a minimum CADR — and then size up rather than down. Add headroom if you live with severe seasonal AQI. Pair that quantity with the right filtration: true HEPA for particles, real activated carbon for smell and gases. Do those few things and you have skipped past nearly every misleading claim on the shelf.
Everything else — quiet operation, smart sensors, app control, a nice display — is genuinely nice to have, but secondary. A purifier with the wrong CADR for your room cannot be rescued by features. A purifier with the right CADR rarely needs them. For the full picture across HEPA grades, coverage and cost, our air purifier buying guide for India is the pillar this article sits under.
[gnr_faq_group title=”CADR and room size, answered”]
[gnr_faq q=”What is a good CADR for a bedroom in India?” a=”For a typical 12×12 ft master bedroom (about 144 sq ft) with a 10 ft ceiling, aim for a CADR of at least 220 m³/hr to get roughly five air changes an hour. If you live in a severe-AQI city like Delhi, size up further so the purifier has headroom on bad winter days.”]
[gnr_faq q=”How do I calculate the CADR I need for my room?” a=”A quick shortcut for a standard 10 ft ceiling: take your room area in square feet and multiply by about 1.5 to get the minimum CADR in m³/hr. So a 200 sq ft room wants roughly 300 m³/hr. For more precise sizing, multiply room volume in cubic metres by five for a five air-changes-per-hour target.”]
[gnr_faq q=”Is a higher CADR always better?” a=”A higher CADR than your room needs is generally a good thing — it lets the purifier run on a lower, quieter speed, use less electricity and extend filter life. The main trade-offs of a bigger machine are a higher upfront price and a larger footprint, so buy enough headroom for your room and city without massively overspending.”]
[gnr_faq q=”Does CADR tell me how well a purifier removes smells?” a=”Not really. CADR mostly measures how much fine particulate the machine clears from the air. Odours and gases are handled by the activated-carbon stage, which CADR does not capture. If kitchen smells, paint fumes or smoke matter to you, look for a genuine, weighty carbon layer alongside a strong CADR.”]
[gnr_faq q=”Will a high-CADR purifier fix the pollution in my city?” a=”No. A purifier cleans the air inside one room. It can make your indoor air markedly cleaner than the air outside, but it does not seal your home or improve the city’s air. On high-AQI days it is a tool to reduce your indoor exposure, not a cure for the season.”]
[/gnr_faq_group]
Still not sure which CADR fits your home? Take our two-minute find your purifier quiz — it weighs your room size, your city’s air and what you are trying to fix, then points you to one honest recommendation. When you are ready to compare models, browse the range on our air purifiers page.
