Blower Door CFM50 Calculator
Building leakage flow at a 50 Pascal test pressure.
Enter your values
ⓘ Live results
Results
- ACH50
- 6
- Natural ACH (n-factor 20)
- 0.3
- Effective leakage rate
- 100 CFM50 per 1000 cu ft
Quick answer
ACH50 equals CFM50 times 60, divided by the building's conditioned volume.
ACH50 = CFM50 x 60 / Volume
How to use the Blower Door CFM50 Calculator
- 1Run a blower door test and record the CFM50 fan flow reading.
- 2Enter the building's conditioned volume.
- 3Read ACH50, the standard airtightness metric used for code compliance.
Worked example
Using the values the calculator loads with:
Inputs
- Blower door CFM50 reading1800 CFM
- Conditioned volume18000 cu ft
Results
- ACH506
- Natural ACH (n-factor 20)0.3
- Effective leakage rate100 CFM50 per 1000 cu ft
Frequently asked questions
What ACH50 is considered tight?
Modern high-performance homes often target 1.0-3.0 ACH50; older leaky homes can exceed 10-15.
What is the n-factor?
It converts test-pressure ACH50 to natural infiltration ACH; 20 is a common simplified assumption, varying with climate and building height.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.