Your lungs clear most of what you breathe, but the finest particles (PM2.5) can reach deep into the lungs — and research suggests some of the tiniest (ultrafine) particles may enter the bloodstream. Here's the practical math: what clean air for your room actually takes, and what it costs to run.
Skip the guesswork. Enter your room and we'll show the clean-air delivery rate (CADR) it needs, which of our picks covers it, and what a year of running one really costs.
Method follows the EPA's guidance on matching CADR to room size.
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How we pick — best for the room, not the most expensive
Main pick — Levoit Vital 200S-P. Our default for a bedroom, living room or nursery: quiet enough to sleep beside (~26 dB in sleep mode), HEPA + carbon, with an air-quality sensor so it only ramps up when it needs to. 4.7★ across ~14,000 reviews. Best for: most homes — and especially households with pets or cats, where fine hair and dander stay airborne and a HEPA filter genuinely captures them. Downside: HEPA and carbon are one bonded filter, so a full filter swap (~$40) every 6–12 months.
Budget pick — Levoit Core 300S-P. The cheapest one we'd actually trust for a single bedroom: same HEPA filtration, app + auto mode, very quiet (down to ~22 dB) — just less airflow (141 CFM CADR) for big open spaces. Best for: one room, tighter budget, renters. Downside: undersized for large open-plan areas, so match the model to the room rather than over- or under-buying.
A purifier lowers airborne particles; it doesn't stop pets shedding or replace cleaning, and no filter "cures" allergies. Ventilation still beats any purifier for CO₂ and cooking fumes — open a window when the air outside is cleaner.
Type your city (or share your location) and we'll pull a modeled outdoor PM2.5 estimate (CAMS) — a snapshot, not a health verdict.
Modeled outdoor data from Open-Meteo (CAMS model, ~11 km grid) — an estimate, not a local sensor reading. It's outdoor air anyway; indoors is usually different, which is why you measure your own room.
You breathe ~22,000 times a day — and the dose depends on where you spend the hours. Across an average lifetime:
So the math is simple: fix the air where you actually spend the hours, and you change the dose that counts. Start with the room you're in most.
Pick your situation — get the exact fix, in three budgets. Every pick is chosen for one thing first: dead-simple to install and use.
A cat hair is far too big to reach your lungs — it gets caught in your nose and throat. The particle that actually matters is invisible: Fel d 1, a sticky allergen from a cat's skin oils and dried saliva, riding on flakes of dander far smaller than pollen.
Because a meaningful fraction of it travels on fine particles (small enough to stay airborne for long periods), it behaves less like falling dust and more like smoke: it stays airborne for hours, drifts from room to room, and settles on every surface — then gets stirred back up the moment you sit down or make the bed. It's so persistent it's measurable even in homes that have never had a cat.
This is exactly the particle a true-HEPA purifier is built to catch. Run one where you and the cat spend the most hours — the bedroom or living room — keep it on, and you lower the airborne load you actually breathe. Pair it with regular washing of bedding and hands.
Honest limits: a purifier lowers airborne allergen-carrying particles, but it can't remove what's already settled in carpets and bedding, doesn't stop shedding, and won't cure a cat allergy. Controlled studies show it reduces airborne allergen but does not guarantee fewer symptoms — if you're allergic, see a doctor.
For cat households, our pick: Levoit Vital 200S-P (for pet hair & airborne dander) →Fel d 1 is the major cat allergen; its size and airborne persistence are documented in home-air studies, and pet-allergen guidance is summarised by the Asthma and Allergy Foundation of America. Estimates here are illustrative, not medical advice.
Exercise isn't optional — it's one of the best things you do for your body. But here's what nobody tells you: a hard workout moves 5-15× more air through your lungs, and you switch from nose- to mouth-breathing — skipping the one filter you were born with. So on a polluted day, the harder you push, the deeper you drive the bad air.
The fix isn't a mask or a gadget on your face (thin evidence). It's simpler: know the number, then choose. Check the air before you head out, run when and where it's clean, and on smog, wildfire or high-pollen days move the session indoors into a HEPA-filtered room. Your motivation stays the same — your dose doesn't have to.
Indoor air simply isn't something anyone measures for you — not at work, not in a hotel, not at home. That's not a conspiracy; it's just nobody's job.
Nobody is hiding it — measuring just isn't part of anyone's job:
The only way to know is to measure it yourself. A monitor (from ~$60 for a basic PM2.5 unit, ~$200+ for multi-sensor models like the ones below) turns an invisible risk into a number you can act on — which is the whole point of everything below.
"Just air the room out" is only right half the time. The honest rule takes 10 seconds:
One indoor monitor + one free outdoor map = every ventilation decision, solved. No second meter needed.
Per kilo of body weight, young children inhale far more air than adults — in the same room, they get a bigger dose of whatever is floating in it. Fresh paint, new furniture, cooking particles, outside smog leaking in: the nursery is where clean air matters most, and it's also the cheapest room to fix.
A child's lungs are still developing, and little ones breathe faster than adults — so clean air in the nursery genuinely matters. The good news: it's also the cheapest room to fix.
One monitor + one small purifier ≈ $180. That's the whole intervention for the room where your child spends 10-12 hours a day.
See the nursery-sized answer (150 sq ft) →Free, no email needed — the full calculation, on one page.
No vibes, no vague "studies show". Each claim, its paper:
Honest disclaimer: the calculator is an engineering estimate (room volume → clean-air delivery → running cost), not a health prediction. Real-world performance varies with fan speed, filter age, doors/windows and where the unit sits. It's here to help you buy the right size and know what it costs to run — not medical advice.
The Air Math is one of four independent tools. Same method, same honesty rules — no fear-selling, sources for every claim, and "you don't need to buy anything" is always an allowed answer.
Run a blog, a forum or an allergy resource? Embed our room-size calculator with one line of code. No cost, no account, no tracking of your readers — and it admits when one unit isn't enough.
Get the embed code →We worked out ten common room sizes in advance — the CADR each one needs, the arithmetic behind it, which unit actually covers it, and the yearly running cost.
Same idea, different purchase. Free, no sign-up, working shown.