Formula & worked example
Q=C_L·A·(P/1 in.wg)^0.65 /100.
Leakage class 4 over 2,000 ft² at 1 in.wg predicts about 80 CFM leakage.
HVAC engineering calculator · Updated Sep 17, 2026
Duct Leakage Calculator — CFM25, Leakage Class & Percent Airflow
Calculate duct leakage from leakage coefficient/class, duct surface area and test pressure, then compare leakage with design airflow.
Inputs
Live result
Predicted leakage 80 CFM
Leakage per 100 ft² 4 CFM
Leakage vs design airflow 0.8%
Assumptions & limits
- Uses the common 0.65 pressure exponent and imperial leakage-class convention.
- Field acceptance limits depend on project specification and duct class.
Frequently asked questions
What does this Duct Leakage Calculator calculate?
Calculate duct leakage from leakage coefficient/class, duct surface area and test pressure, then compare leakage with design airflow.
Is this suitable for final equipment selection?
Use it as an auditable engineering cross-check. Final selections should use measured design conditions, manufacturer data, applicable standards and local code.
Why does MAXScanner expose the assumptions?
HVAC shortcuts can hide density, pressure, concentration and effectiveness assumptions. Exposing them makes the result easier to verify and revise.