Find the right CADR rating for your room by entering length, width, height, and desired ACH. Includes formulas, and a full example. Ideal for choosing the perfect air purifier for bedrooms, living rooms, and offices.
Choosing the right air purifier depends mainly on the room size and the ACH (Air Changes per Hour) you want. This calculator helps you find the required CADR (Clean Air Delivery Rate) — the official rating that tells you how powerful an air purifier needs to be for your room.
Formulas Used in the Calculator
1 Room Volume Formula
Room Volume=Length×Width×Height
2 Required CADR Formula
CADR (Clean Air Delivery Rate) measures how much clean air the purifier must deliver each minute.
CADR=60Room Volume×ACH
3 Recommended Air Purifier Size
For simplicity, the “recommended purifier size” is the minimum CADR the user needs:
Recommended Purifier CADR≥CADR
Example Calculation
Let's take a real example:
- Room Length: 15 ft
- Room Width: 12 ft
- Room Height: 8 ft
- ACH: 5 (recommended for allergies)
Step 1 — Calculate Room Volume
Room Volume=15×12×8=1440 ft3
Step 2 — Calculate Required CADR
CADR=601440×5=120 CFM
Final Recommendation:
Your room requires an air purifier with at least:
CADR≥120 CFM
FAQs
1. How do I calculate the right air purifier size for my room?
To size an air purifier correctly, calculate your room volume (length × width × height) and multiply it by your desired ACH (Air Changes per Hour). Divide by 60 to get the required CADR (CFM). An air purifier with that CADR or higher is suitable for your room.
2. What is CADR and why is it important?
CADR (Clean Air Delivery Rate) tells you how much filtered air an air purifier can deliver per minute. A higher CADR means faster cleaning. Choosing a purifier with the correct CADR ensures it can clean your room effectively.
3. What is ACH in air purification?
ACH stands for Air Changes per Hour and indicates how many times the air purifier cleans the entire room air in one hour. Higher ACH ratings are recommended for allergy sufferers or heavily polluted rooms.
4. How many ACH do I need?
- Normal use: 4–6 ACH
- Allergies/Asthma: 6–10 ACH
- Smoke, pollution, wildfire: 8–12 ACH
- Choose a higher ACH if you want faster or deeper purification.
5. Does ceiling height affect air purifier size?
Yes. Rooms with higher ceilings have more air volume, so they require purifiers with higher CADR to clean the air effectively. That's why volume (not just area) is important.
6. Can a small air purifier work in a large room?
It may run, but it won’t clean the entire room effectively. It will take longer, may not reach the desired ACH, and may not remove pollutants fast enough. Always size the purifier based on room calculations.
7. Is it better to choose an air purifier larger than required?
Yes, choosing a slightly larger purifier (higher CADR) is usually beneficial. It cleans the room faster, runs more quietly at lower fan speeds, and offers better purification for allergens and smoke.
8. What happens if the air purifier is too large for my room?
Nothing harmful — it just works more efficiently and often more quietly. There is no downside to choosing a purifier with a higher CADR than required.
9. Do two small air purifiers equal one large purifier?
Yes, two purifiers in the same room can add their CADR values together. For example, two purifiers with 60 CFM each are similar to one purifier with 120 CFM.
10. Should door openings or connected rooms be included?
If the room is open to hallways or other spaces, treat the entire open area as one room. Calculate the total volume; otherwise, the purifier may be undersized.
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