Blower Door CFM50 Calculator
Building leakage flow at a 50 Pascal test pressure.
Enter your values
Enter the blower door cfm50 reading in CFM.
Enter the conditioned volume in cu 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.
- 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
At a glance
| What it does | Building leakage flow at a 50 Pascal test pressure. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Blower door CFM50 reading, Conditioned volume |
| Main output | ACH50 |
| Formula | ACH50 = CFM50 x 60 / Volume |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Blower door CFM50 reading(CFM)
- Enter the blower door cfm50 reading in CFM.
- Conditioned volume(cu ft)
- Enter the conditioned volume in cu ft.
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.
What do I need to enter into the Blower Door CFM50 Calculator?
Just 2 values: blower door cfm50 reading, conditioned volume. 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 Blower Door CFM50 Calculator work out the answer?
ACH50 equals CFM50 times 60, divided by the building's conditioned volume. It applies the formula ACH50 = CFM50 x 60 / Volume and shows the working so you can check each step by hand.
Is the Blower Door CFM50 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.