Quick answer
A 200 CFM air purifier covers about 313 sq ft / 29.0 m2 at 4.8 ACH with an 8 ft ceiling. Two identical units raise the estimate to about 625 sq ft.
How to use this air purifier room size calculator
Find the purifier's smoke CADR in the product specifications. Enter that CADR, the ceiling height, and the clean-air target you want. The calculator estimates the maximum floor area that CADR can support.
Use the everyday AHAM-style target for normal particle cleaning. Use a higher smoke or custom target when planning for wildfire smoke, heavy pollution, or faster filtration.
If you already know the room size and need the required CADR instead, use the Air Purifier CADR Calculator. If you plan to combine different purifier models in one open room, use the Multiple Air Purifiers ACH Calculator. After checking room fit, compare operating cost with the Air Purifier Electricity Cost Calculator and the Air Purifier Filter Replacement Cost Calculator.
Air purifier room size formula
total CADR = CADR per purifier x number of purifiersmaximum room volume = total CADR (CFM) x 60 / target ACHmaximum room area = maximum room volume / ceiling heightAHAM 2/3 rule area = CADR / (2 / 3), or CADR x 1.5The main formula uses room volume and target air changes per hour. The AHAM 2/3 rule is included as a simple reference for standard rooms, but ceiling height and target ACH give a clearer estimate.
Assumptions and methodology
This calculator estimates particle-cleaning room size from CADR. It assumes the purifier is running at the speed that produces the listed CADR and that the room is reasonably open.
- CADR values can be added only as a rough estimate when multiple units clean the same open room.
- Taller ceilings reduce the maximum floor area for the same CADR because the room contains more air volume.
- Higher ACH targets reduce room size but increase how quickly particles are filtered.
- Doorways, partitions, blocked airflow, low fan speed, and noise limits can reduce real-world coverage.
Example calculations
200 CADR room size example
A 200 CFM purifier at 4.8 ACH with an 8 ft ceiling covers about 313 sq ft / 29.0 m2. That is a practical bedroom, office, or medium-room estimate.
If the same purifier is used for smoke-heavy planning at 7.5 ACH, the estimate drops to about 200 sq ft. Two identical 200 CFM units in one open room roughly double the CADR and cover about 625 sq ft at the everyday target.
Air purifier CADR room size chart
This chart assumes one air purifier, an 8 ft ceiling, and a 4.8 ACH everyday target. Use the calculator above for taller ceilings, multiple units, or smoke-heavy planning.
| Smoke CADR | Total CADR | ACH-based room size | AHAM 2/3 rule | Smoke-heavy estimate |
|---|---|---|---|---|
| 80 CFM | 80 CFM | 125 sq ft / 11.6 m2 | 120 sq ft / 11.1 m2 | 80 sq ft / 7.4 m2 |
| 120 CFM | 120 CFM | 188 sq ft / 17.4 m2 | 180 sq ft / 16.7 m2 | 120 sq ft / 11.1 m2 |
| 150 CFM | 150 CFM | 234 sq ft / 21.8 m2 | 225 sq ft / 20.9 m2 | 150 sq ft / 13.9 m2 |
| 200 CFM | 200 CFM | 313 sq ft / 29.0 m2 | 300 sq ft / 27.9 m2 | 200 sq ft / 18.6 m2 |
| 250 CFM | 250 CFM | 391 sq ft / 36.3 m2 | 375 sq ft / 34.8 m2 | 250 sq ft / 23.2 m2 |
| 300 CFM | 300 CFM | 469 sq ft / 43.5 m2 | 450 sq ft / 41.8 m2 | 300 sq ft / 27.9 m2 |
| 400 CFM | 400 CFM | 625 sq ft / 58.1 m2 | 600 sq ft / 55.7 m2 | 400 sq ft / 37.2 m2 |
| 600 CFM | 600 CFM | 938 sq ft / 87.1 m2 | 900 sq ft / 83.6 m2 | 600 sq ft / 55.7 m2 |
What to check before trusting a room-size claim
Product room-size claims can be based on different assumptions. A claim may use a standard 8 ft ceiling, a lower ACH target, or a specific fan speed. Always compare the actual smoke CADR, not only the marketing square-foot number.
If a purifier seems undersized for the room, you can choose a higher CADR model, use multiple units in one open space, or accept a lower ACH target. For bedrooms, also consider noise at the fan speed needed to reach the listed CADR.
Related calculators
AC Room Size Calculator
Estimate what room size an air conditioner can cool based on BTU or kW capacity.
Air Purifier CADR Calculator
Estimate the smoke CADR an air purifier needs from room dimensions, ceiling height, and target air changes per hour.
Multiple Air Purifiers ACH Calculator
Estimate combined air changes per hour from multiple air purifiers, room size, ceiling height, and target ACH.
Air Purifier Filter Replacement Cost Calculator
Estimate annual air purifier filter replacement cost from filter price, replacement interval, room conditions, and number of units.
Air Purifier Electricity Cost Calculator
Estimate air purifier electricity cost from watts, daily runtime, annual kWh, electricity price, and number of units.
Dehumidifier Size Calculator
Estimate dehumidifier capacity in pints per day or liters per day from room size, dampness level, ceiling height, and space type.
FAQ
What room size can a 200 CADR air purifier cover?
With an 8 ft ceiling and a 4.8 ACH target, a 200 CFM air purifier covers about 313 sq ft / 29.0 m2. A smoke-heavy target lowers that to about 200 sq ft.
How do I calculate air purifier room size from CADR?
Convert CADR into room volume by multiplying CADR in CFM by 60 and dividing by the target air changes per hour. Then divide the room volume by ceiling height to get floor area.
What is the AHAM 2/3 rule for air purifier room size?
A common AHAM-style shortcut is to choose a smoke CADR that is about two-thirds of the room area in square feet for a standard 8 ft ceiling. Reversing that rule gives room area of about CADR multiplied by 1.5.
Does ceiling height change air purifier coverage?
Yes. A taller ceiling means more air volume for the same floor area, so the same CADR covers fewer square feet at the same ACH target.
Can I add CADR from two air purifiers?
For a single open space, you can roughly add the smoke CADR of identical units if both run at the same time and airflow is not blocked. Separate rooms, doors, partitions, and poor placement reduce the value of simply adding CADR.
Should I use smoke CADR, dust CADR, or pollen CADR?
Use smoke CADR for room-size planning when available. Smoke CADR is usually the conservative particle-cleaning number and is easier to compare across models.
Why does smoke or wildfire use need a smaller room size?
Smoke-heavy use often needs a higher clean-air target, so the same CADR is spread over less room volume. That is why the smoke-heavy estimate is smaller than the everyday AHAM-style estimate.
Is CADR room size the same as odor removal?
No. CADR mainly describes particle cleaning. Odors, gases, VOCs, and some smoke odors depend on activated carbon, source control, ventilation, and filter design.