Air purifier calculator

Estimate the clean-air delivery your room needs from its volume and target air changes per hour.

Published 11 October 2026

Room-sizing calculator

Room size preset

Editable estimates with a 2.6 m ceiling, not official HDB room sizes. Open concept includes connected living, dining and kitchen space. Check your actual dimensions.

Enter room size Room volume Length, width & height

Room volumeVolume unit

Target ACH

My preference: 20 ACH, based on my experience during the 2014 haze, when two 400 m³/h CADR purifiers in a common bedroom felt about right.

NEA’s haze guide (2014, Annex A) recommends smoke CADR of at least 3 × room volume in m³, expressed in cfm. This corresponds to ≈ 5.1 clean-air changes per hour.

Filter degradation allowance (%)

Assumed overall CADR loss. EOL means end of life; these are planning allowances based on the sources alongside.

Dyson HushJet electret filter: Dyson uses a 50% decline in CADR as the endpoint for its filter-life test.

2017 paper: cites a bedroom HEPA purifier with 25% lower CADR after 800 hours of intermittent use.

2024 study: Winix C535 CADR declined by 26.8% at higher simulated dust loads, tested up to 46 g.

Minimum clean-filter CADR (estimate)

Enter your room volume to calculate.

Room volume × target ACH = required clean-air delivery.

Enable JavaScript to use the calculator, or multiply room volume in m³ by target ACH, then divide by (1 − loss percentage ÷ 100) to get the required clean-filter CADR in m³/h. Convert ft³ to m³ by multiplying by 0.028316846592.

Use the estimated CADR to compare purifiers at the fan speed you will actually use. For haze, look for a smoke CADR result; raw airflow does not account for cleaning performance.

This is a room-sizing estimate, not a guarantee during haze. See the model comparison for performance and noise.

Suggested models

Settings from the model comparison, with at least five models shown. Settings that meet your required clean-filter CADR appear first; larger alternatives fill any remaining places. If none meet it, the 10 largest models appear. Check the listed fan speed and noise before choosing.

Enter your room size above to see matching models.

Model / source	Fan setting	CADR (m³/h) / method	Noise / source
LG PuriCare AeroBooster AS55GGSY0Singapore manufacturer	High (assumed CADR pairing)	411; manufacturer rating, pollutant and test method unspecified	52 dB Published · Singapore
Sharp FX-S120E-HSingapore	High	741 smoke; GB/T 18801-2022	54 dB; Published · Singapore
Sharp FX-S120E-HSingapore	Medium	≈386; airflow-based estimate	< 37 dB (fan spec) Published · Singapore
Sharp FX-S120E-HSingapore	Low	≈139; airflow-based estimate	< 20 dB (fan spec) regional verification needed Published · Singapore
Dyson HushJetmanufacturer	High	≈223; manufacturer rating, method unspecified	42 dB; weighting unverified Published
Dyson HushJetRTINGS	High / maximum	250; independent PM1 test	53.7 dBA; per research file RTINGS
Xiaomi Smart Air Purifier 4 Litemanufacturer	High	360 particles; GB/T 18801-2015	≤61 dBA Published
Xiaomi Smart Air Purifier 4 LiteBreatheSafeAir	High / maximum	350; independent room test	58 dBA BreatheSafeAir
Xiaomi Smart Air Purifier 4 LiteBreatheSafeAir	Half speed (50%)	155; independent room test	44 dBA BreatheSafeAir
Mijia Smart Air Purifier 6 PlusSingapore AC-M35-SC	Maximum (CADR pairing assumed)	810 particles; manufacturer-reported CVC test, WTS2026-3401-1; test standard unspecified	≤66 dB(A); official global FAQ Published · Singapore AC-M35-SC
Mijia Smart Air Purifier MaxSingapore AC-M34-SC	Maximum (CADR pairing assumed)	1,006.5 particles; manufacturer-reported Guangzhou Institute test, KJ2025003538E; test standard unspecified	≤68 dB(A); official global FAQ Published · Singapore AC-M34-SC
Mijia Smart Air Purifier 6Singapore AC-M25-SC	High	443 particles; Singapore tested value, report KJ2025001525E; test standard unspecified	64 dBA; UK FAQ figure, Singapore maximum noise unverified Published · Singapore AC-M25-SC
Smart Air SqairBreatheSafeAir	Speed 1 / Low	65; manufacturer rating quoted in review, method unspecified	Not numerically reported BreatheSafeAir
Smart Air SqairBreatheSafeAir	Speed 2 / Medium	180; manufacturer rating quoted in review, method unspecified	Not numerically reported BreatheSafeAir
Smart Air SqairBreatheSafeAir	Speed 3 / High	315; manufacturer rating quoted in review, method unspecified	Not numerically reported BreatheSafeAir
Smart Air QT3BreatheSafeAir	Speed 3 / High	37; manufacturer rating quoted in review, method unspecified	63 dBA; reviewer measurement BreatheSafeAir
Xiaomi Smart Air Purifier 4 CompactBreatheSafeAir	High / maximum	216; independent room test, median of 3 runs	56 dBA; reviewer measurement BreatheSafeAir
Xiaomi Smart Air Purifier 4 CompactBreatheSafeAir	Half speed (50%)	141; independent room test, median of 3 runs	45 dBA; reviewer measurement BreatheSafeAir
Dyson Purifier Big+Quiet Formaldehyde BP04RTINGS	Speed 10 / maximum	329; independent PM1.0 room test, RTINGS methodology v1.3.1	47.6 dBA; RTINGS noise test at 25 in (≈0.64 m) RTINGS
Daikin MCK70ZVM7international manufacturer	Turbo	375; manufacturer conversion from JEM1467 test values	54 dB; regional suffix unverified Published · international
Daikin MC80ZVM7international manufacturer	Turbo	480; manufacturer rating, test method unspecified	55 dBA; regional suffix unverified Published · international

Matching results show each source series’s lowest listed CADR setting that meets the target. The largest-model list uses each model’s highest listed CADR. Ratings, independent tests and estimates use different methods; this is a sizing shortlist, not a performance ranking. Source links retain each result’s caveats. Models without a numeric CADR are not included.