What Is CADR? Air Purifier Ratings Explained

CADR in plain terms

CADR stands for Clean Air Delivery Rate: the volume of clean, filtered air a purifier pushes out per hour. In Singapore it is almost always quoted in cubic metres per hour (m³/h). A CADR of 300 m³/h means the unit delivers 300 cubic metres of filtered air every hour at full speed.

Some US-market listings quote CADR in cubic feet per minute (cfm) instead. Multiply a cfm figure by about 1.7 to convert it to m³/h before you compare anything.

The key point: CADR is a speed rating, not a quality rating. It tells you how quickly a purifier can turn over the air in a room — which is why it is the single most important number for matching a purifier to your room size, and almost useless for anything else.

The CADR-to-room-size rule

Sizing a purifier is simple arithmetic:

Required CADR (m³/h) = floor area (m²) × ceiling height (m) × target air changes per hour (ACH)

ACH is how many times the room's full volume of air passes through the purifier each hour. Sensible targets by setting:

• Homes: 3–4 ACH
• Offices: 4–5 ACH
• Clinics: 5+ ACH
• Dental and procedure rooms: 6+ ACH

Public-health guidance since the pandemic (including the US CDC) recommends targeting at least 5 air changes per hour of clean air in occupied spaces — a good benchmark for any room where people gather. If you would rather skip the maths, our air purifier size calculator gives you the exact figure for your room in seconds.

Worked examples: HDB bedroom, living room, clinic consult room

Assume a typical ceiling height of about 2.6 m and the formula becomes very concrete:

• HDB bedroom (~10 m²): 10 × 2.6 × 4 ACH ≈ 105 m³/h. A compact unit covers this easily.
• HDB living and dining area (~21 m²): 21 × 2.6 × 4 ACH ≈ 220 m³/h.
• Clinic consultation room (~12 m²): 12 × 2.6 × 6 ACH ≈ 190 m³/h.
• Clinic waiting room (~30 m²): 30 × 2.6 × 5 ACH ≈ 390 m³/h.

Notice how the same floor area needs a very different CADR depending on the setting. A 12 m² bedroom needs barely 100 m³/h, while a 12 m² consult room where patients rotate through all day needs nearly double, because infection control calls for a higher air-change target. For clinical settings, our clinic air purifier guide goes into room-by-room detail.

Matching CADR to real rooms: the AIRE lineup

Here is how those numbers map onto our own range — every AIRE room purifier uses H13 medical-grade HEPA as standard:

Run the numbers and the fit becomes obvious. The Fillo Plus's 300 m³/h in a 12 m² consult room works out to more than 9 air changes per hour — comfortably above the 6+ ACH benchmark for procedure rooms. The Classic 400S's 480 m³/h clears the 390 m³/h a 30 m² waiting room needs, with headroom to spare. You can browse the full range on our products page.

What CADR does not tell you

Here is the honest part most spec sheets skip: CADR measures one thing only — how fast a purifier removes particles from the air. It says nothing about three factors that matter just as much:

• Gases and odours. VOCs, formaldehyde off-gassing from new renovation materials and cooking smells are molecules, not particles, so CADR ignores them entirely. That job belongs to the activated carbon layer.
• Filter grade. Two purifiers can share the same CADR while capturing very different fractions of the finest particles. H13 is defined under EN 1822 as capturing at least 99.95% of particles at the most-penetrating particle size — our H13 vs ordinary HEPA comparison explains why that grade matters.
• What happens to trapped microbes. Capturing a bacterium is not the same as neutralising it. In chamber testing, AIRE's active sterilisation — UV-C light plus copper-silver ion technology — eliminated more than 99.99% of tested airborne pathogens (E. coli, Staphylococcus albus, Influenza A) within 60 minutes, versus roughly 4 hours 23 minutes for the same organisms to decay passively on a standard HEPA filter. CADR captures none of this; the distinction is the subject of our purifier vs steriliser guide.

So use CADR to shortlist by room size first, then compare filter grade, carbon capacity and sterilisation to choose between the shortlisted units.

A quick buying checklist

1. Calculate your required CADR from floor area, ceiling height and the right ACH target for your setting.
2. Buy headroom. Quoted CADR is measured at maximum fan speed, which is rarely how you will run the unit day to day. A purifier with spare capacity hits your target ACH at a quieter mid speed.
3. Check noise at the speed you will actually use — especially for bedrooms and consult rooms where conversation or sleep matters.
4. For clinics and childcare settings, look beyond CADR to filter grade and active sterilisation, since reducing airborne load is the real goal.

Still unsure which CADR band your space falls into? We offer a free 30-day pilot with zero upfront cost: we place a right-sized unit in your actual room, and at the end you buy, rent or return it. WhatsApp or call us at +65 8082 3699 and we will size it with you.

Frequently asked

Is a higher CADR always better?

Not automatically — the goal is meeting the required CADR for your room, calculated from floor area, ceiling height and target air changes per hour. A unit with headroom above that number is genuinely useful, because it can run at a lower, quieter fan speed while still hitting the target. What you want to avoid is a CADR below your room's requirement, because the purifier will simply never keep up.

What CADR do I need for an HDB bedroom?

A typical 10 m² HDB bedroom with 2.6 m ceilings needs roughly 105 m³/h to achieve 4 air changes per hour. Any unit rated around 200 m³/h or above covers this comfortably at a quiet, sleep-friendly speed. Our size calculator gives the exact figure for your own room dimensions.

Does CADR tell me anything about viruses or bacteria?

No. CADR measures how quickly particles are removed from the air, and says nothing about whether trapped microorganisms are neutralised. That is a separate function — in AIRE units, UV-C light and copper-silver ion technology actively sterilise what the H13 filter captures.

Why is CADR sometimes shown in cfm instead of m³/h?

US-market listings often use cubic feet per minute (cfm), while Singapore listings use cubic metres per hour (m³/h). Multiply a cfm figure by about 1.7 to convert it to m³/h. Always compare in the same unit — a rating of 300 in cfm describes a far more powerful machine than 300 in m³/h.

Related reading

• Do Air Purifiers Actually Work? An Honest Answer
• Air Purifier vs Air Steriliser: What's the Difference?
• Medical-Grade vs Consumer Air Purifiers: The Real Difference