Air Purifier CADR to ACH Calculator
Air changes per hour from a purifier's CADR rating.
Enter your values
Enter the cadr rating in CFM.
Enter the room area in sq ft.
Enter the ceiling height in ft.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Air changes per hour
- 11.25
- Room volume
- 1,600 cu ft
- Assessment
- Good for general air cleaning (5+ ACH)
Quick answer
Air changes per hour equal the purifier's CADR in CFM multiplied by 60 and divided by the room volume.
ACH = CADR x 60 / room volume
At a glance
| What it does | Air changes per hour from a purifier's CADR rating. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | CADR rating, Room area, Ceiling height |
| Main output | Air changes per hour |
| Formula | ACH = CADR x 60 / room volume |
| Cost | Free — no sign-up, no download |
How to use the Air Purifier CADR to ACH Calculator
- 1Find the purifier's CADR rating (usually for smoke, dust or pollen in CFM).
- 2Compute the room volume from area and ceiling height.
- 3Multiply CADR by 60 and divide by volume to get ACH.
Inputs explained
- CADR rating(CFM)
- Enter the cadr rating in CFM.
- Room area(sq ft)
- Enter the room area in sq ft.
- Ceiling height(ft)
- Enter the ceiling height in ft.
Worked example
Using the values the calculator loads with:
Inputs
- CADR rating300 CFM
- Room area200 sq ft
- Ceiling height8 ft
Results
- Air changes per hour11.25
- Room volume1,600 cu ft
- AssessmentGood for general air cleaning (5+ ACH)
Frequently asked questions
What ACH is considered good?
4-6 ACH is a common target for general indoor air quality improvement; 5-8 for infection control support.
CADR vs HEPA ACH claims?
CADR already accounts for filter efficiency and fan speed, making it the most realistic comparison metric.
What do I need to enter into the Air Purifier CADR to ACH Calculator?
Just 3 values: cadr rating, room area, ceiling height. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Air Purifier CADR to ACH Calculator work out the answer?
Air changes per hour equal the purifier's CADR in CFM multiplied by 60 and divided by the room volume. It applies the formula ACH = CADR x 60 / room volume and shows the working so you can check each step by hand.
Is the Air Purifier CADR to ACH Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.