Enter the airflow in cubic feet per minute (CFM) and select the duct cross-section to estimate the dynamic pressure in pounds per square inch (PSI). This converter uses standard HVAC velocity-pressure relationships for air at typical conditions.
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CFM to PSI Formula
The following formula is used to estimate the dynamic pressure in PSI from airflow in CFM and duct cross-sectional area.
\psi \approx 0.0361 \left(\frac{CFM}{4005A}\right)^2Variables:
- ψ is the estimated dynamic pressure in PSI
- CFM is the airflow in cubic feet per minute
- A is the duct cross-sectional area in square feet
To calculate the estimated dynamic pressure, first divide the airflow by the duct area to determine the air velocity in feet per minute. Then use the HVAC relationship vp (inH₂O) = (V / 4005)² and convert inches of water column to PSI using 1 inH₂O ≈ 0.0361 PSI.
What is CFM to PSI Conversion?
CFM and PSI are different physical quantities. CFM measures volumetric airflow, while PSI measures pressure. Because of this, there is no single direct conversion factor between them. Instead, the conversion must be estimated using fluid-dynamic relationships that depend on airflow velocity, duct area, and air density. In HVAC applications, this typically means converting the airflow into velocity and then estimating the resulting dynamic or velocity pressure.
This converter estimates dynamic pressure only. It does not calculate compressor discharge pressure, line pressure, or total static pressure. The result is most useful for understanding how airflow and duct size affect air velocity and pressure behavior in ducts.
How to Calculate CFM to PSI?
The following steps outline how to estimate PSI from CFM for airflow in a duct.
- First, determine the airflow rate in cubic feet per minute (CFM).
- Next, determine the duct cross-sectional area in square feet (A).
- Calculate the average air velocity using V = CFM ÷ A.
- Compute the velocity pressure in inches of water using vp = (V / 4005)².
- Convert the result to PSI using PSI ≈ vp × 0.0361.
- After inserting the values and calculating the result, check your answer with the converter above.
CFM to PSI Conversion Table (1000 CFM Examples)
The table below shows estimated dynamic pressure in PSI for 1000 CFM flowing through several common duct cross-sections.
| Duct Area | Velocity (ft/min) | Estimated Pressure (PSI) |
|---|---|---|
| 0.25 ft² (≈ 6 in round) | 4000 | 0.0360 |
| 0.5 ft² (≈ 8–9 in round) | 2000 | 0.0090 |
| 1.0 ft² (≈ 12 × 12 in) | 1000 | 0.0023 |
| 2.0 ft² (≈ 18 × 16 in) | 500 | 0.0006 |
These values represent velocity pressure only, which is usually much smaller than compressor pressure or many static pressure values in a system. Even so, this relationship is very useful when estimating duct performance, fan behavior, and airflow effects.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Airflow (CFM) = 1000
Duct Area (A) = 1.0 ft²
Velocity (V) = 1000 ft/min
Estimated Dynamic Pressure (ψ) ≈ 0.0023 PSI