Guidance only. Actual performance depends on the confirmed SKU CADR, sealing, filter grade and fan setting. For a defensible spec, we quote the model's tested CADR (AHAM AC-1 or GB/T 18801) in writing.
After sizing, place it right: the same unit delivers 50–80% allergen reduction in an open spot versus 20–30% in a corner — see where to place an air purifier.
How the calculation works
There are two accepted ways to size an air purifier, and they agree with each other.
1. AHAM two-thirds rule
The Association of Home Appliance Manufacturers (AHAM) publishes the CADR standard and recommends that a purifier's CADR in CFM be at least two-thirds of the room's floor area in square feet, assuming a standard 8 ft ceiling. A 300 ft² room therefore wants a CADR of at least 200 CFM. It is a fast rule of thumb printed on the AHAM Verifide seal.
2. Air changes per hour (ACH)
The more flexible method sizes by how many times per hour you want the room's full air volume filtered:
Required CADR (m³/h) = room area × ceiling height × target ACH
(then divide by 1.699 to convert m³/h to CFM)
The AHAM two-thirds rule works out to about 5 air changes per hour at an 8 ft ceiling, which is why the two methods line up. Choose your ACH by need:
| Use case | Air changes/hour | Why |
|---|---|---|
| General comfort | ~2 | Everyday dust and light odor control. |
| Allergy / asthma / dust | 4–5 | Faster turnover keeps fine-particle levels low for sensitive users. |
| Smoke / wildfire / VOC / pets | 5–6 | Heavy or continuous pollutant loads need more passes; the US EPA advises higher exchange during smoke events. |
| Commercial / clinical / crowded | 6+ | High occupancy and aerosol-sensitive rooms want the highest turnover. |
Sources: AHAM Verifide — CADR directory; US EPA — air cleaners in the home. Conversion: 1 CFM = 1.699 m³/h.
What the result means for an OEM order
If you are sourcing a private-label line, the calculated CADR tells you which model class to spec for each target room size — and lets you build an honest room-coverage claim on the box:
- Small rooms / desktop SKUs (bedrooms, offices): lower CADR, compact bodies — see desktop OEM.
- Living rooms / mid–large spaces: higher-airflow towers — see tower OEM.
- Halls, clinics, offices at scale: high-CADR or multi-unit — see commercial OEM.
We do not publish inflated coverage numbers: every model's CADR comes from its AHAM AC-1 or GB/T 18801 test report, and we help you word the room-size claim so it survives a marketplace or customs check.
Need the tested CADR for a specific model?
Tell us your target room sizes and markets — we will match the model class, share the CADR test report, and quote MOQ and lead time.
Request Model & CADR ReportFrequently asked questions
How do I calculate the CADR I need for a room?
Use either method above. The AHAM two-thirds rule (CADR in CFM ≥ two-thirds of ft²) is fastest; the ACH method (volume × air changes per hour) is more precise for non-standard ceilings and heavy pollutant loads. They agree because the two-thirds rule equals about 5 ACH.
What is a good air changes per hour for an air purifier?
About 2 ACH for general comfort, 4–5 for allergy and asthma, and 5–6 or more for smoke, VOCs, pets or crowded commercial rooms.
How do I convert CADR between CFM and m³/h?
One CFM equals 1.699 m³/h. Multiply CFM by 1.699 for m³/h, or divide m³/h by 1.699 for CFM. Always check which standard a number uses — AHAM AC-1 reports CFM, China GB/T 18801 reports m³/h.
Related guides
- EPA wildfire-smoke CADR rule — the 2/3 baseline versus AHAM's stronger wildfire target.
- CADR vs CCM — cleaning speed vs filter life.
- AHAM vs GB/T 18801 — reading a CADR test report.
- Large-room air purifiers — high-CADR configurations.
- Air purifier models — browse the OEM/ODM range.
General sizing guidance, not a performance guarantee. Confirm the model's tested CADR and standard before publishing any room-coverage claim.
