Air Changes Per Hour (ACH) Calculator

This tool helps you calculate how many times the air in your room is completely filtered by your air purifier each hour. Achieving the right ACH is crucial for maintaining clean and healthy indoor air.

Calculate Your ACH

ACH Calculator

Room Dimensions

Room Area (sq. ft.)

Ceiling Height: 8 ft

Air Purifier's CADR (CFM)

ACH Result:

0.0 ACH

Time to Clean Air:

-- min

Enter your data for a detailed result.

What Your ACH Number Means

Your ACH result tells you how effective your air purification is. Here are the standard industry recommendations:

ACH = (CADR in CFM × 60) / (Room Area × Ceiling Height)

Good (2-3 ACH)

Best for maintaining general air freshness and controlling light dust in a standard room.

Excellent (4-5 ACH)

This meets the AHAM standard. It's highly recommended for people with allergies, pet dander issues, or sensitivity to mold spores.

Superior (6-8+ ACH)

This level provides critical air purification for spaces with smoke, VOCs, wildfire smoke, or for individuals with severe allergies and mold issues.

Why is ACH So Important?

When I first started researching purifiers for my son’s allergies, I was obsessed with CADR (Clean Air Delivery Rate). But I soon realized that a powerful air purifier is useless in the wrong-sized room. The real metric that matters is ACH. It tells you if your purifier is actually doing its job for your specific space. An ACH of 5 means the entire volume of air in your room is being cleaned once every 12 minutes. To fight allergens and mold, this consistent filtration is absolutely essential.