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. Enter the full room volume and choose a planning target; the result is not a prediction of indoor pollution.

Room length (ft)

Room width (ft)

Ceiling height (ft)

Planning clean-air changes/hour

Recommendation

Look for at least 160 m³/h CADR

Mid-range bedroom unit · Typical spend ₹11,000 - ₹15,000

Room: 120 sq ft (11 m²)

Calculated CADR: 153 m³/h

Room volume: 30.6 m³

Clean-air target: 5 changes/hour

Formula: length × width × height in feet × 0.02831685 × clean-air changes/hour. The shopping target rounds up to 10 m³/h. Include connected open spaces; leakage, sources and fan speed affect actual performance. This tool does not predict or guarantee an indoor PM2.5 level. See the EPA sizing guide.

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?

CADR (m³/h) = room area (m²) × ceiling height (m) × target clean-air changes per hour. At a planning target of 5 changes/hour, a 15 m² room with a 3 m ceiling needs 225 m³/h. Check the CADR at a fan speed you can tolerate, and account for open doors and ongoing pollution. This is a sizing calculation, not a prediction of indoor PM2.5.

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.