Free tool

Air Purifier CADR Calculator: What Size Do You Actually Need?

What CADR does your room need?

CADR (clean air delivery rate, m³/h) is the number that decides whether an air purifier actually works in your room. Manufacturer coverage claims assume sealed rooms — this calculator adjusts for real conditions.

Room length (ft)

Room width (ft)

Typical outdoor AQI

Recommendation

Look for at least 90 m³/h CADR

Compact bedroom unit · Typical spend ₹9,000 - ₹12,000

Room: 120 sq ft (11 m²)

Baseline CADR: 56 m³/h (5× floor area)

Pollution multiplier: ×1.6

Realistic indoor target: under 25 µg/m³ PM2.5

Assumptions: 2.7 m ceiling, door closed, no continuous indoor pollution source. If your room opens onto a hall or kitchen, treat the combined space as the room. One purifier cannot clean a whole flat.

See matching air purifiers Read the buying guide

Most disappointment with air purifiers traces to one mistake: buying a unit rated for the room's floor area rather than for the room's floor area plus the reality of Indian conditions. Manufacturer coverage figures are measured in sealed chambers with no ongoing pollution source. Your bedroom has a door that opens, a window that leaks, and a city outside.

The second mistake is buying one large unit for the whole home. It feels efficient and it does not work — purified air does not migrate meaningfully between rooms against normal air movement. If your budget is ₹30,000, two ₹13,000 units covering two bedrooms will reduce your family's actual exposure far more than one ₹30,000 unit in the drawing room.

Use the calculator, then verify after you buy: note the PM2.5 reading, close the room, run on high for 40 minutes, and watch the number fall. If it does not drop substantially, the unit is undersized, the filter is exhausted, or outside air is leaking in.

Frequently asked questions

What CADR do I need for my room?

As a rule of thumb, CADR in m³/h should be at least 5× your room's floor area in square metres — so a 160 sq ft (15 m²) bedroom needs at least 75 m³/h. Then size up one class in normal cities and two classes in very high-pollution cities, because manufacturer coverage figures assume a sealed room with no ongoing pollution source.

Why should I ignore the coverage area printed on the box?

Because it is measured under ideal conditions — a sealed room of exactly that size, doors closed, no continuous pollution source. Real Indian homes have open doorways, cooking, street dust and window leakage. Treat claimed coverage as an optimistic ceiling rather than a specification.

Is one air purifier enough for my whole home?

No. Purified air does not travel usefully between rooms against normal air movement, so one unit cleans one room. Buy one per closed room you actually spend time in, prioritised by hours — bedrooms first. For most families, two mid-range units across two bedrooms beat one premium unit in the hall.

Not sure what you actually need? Ask us before you spend.

Tell us your city, your water source and your budget. For homes we will recommend the right technology — including telling you when a ₹3,000 purifier is genuinely enough. For offices, societies and factories, our team will size a system against your water report and send a specification-backed quotation.

Or email betterworkindia@gmail.com — attach a water analysis report and we can quote faster.