Venturi Flow Calculator
Airflow from a venturi meter's throat differential pressure.
Enter your values
Enter the inlet pipe diameter in in.
Enter the throat diameter in in.
Enter the differential pressure in in wc.
Enter the discharge coefficient you are working with.
Enter the air density in lb/ft3.
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.
- Airflow
- 252 CFM
- Throat velocity
- 21.4 ft/s
- Beta ratio
- 0.6
Quick answer
Venturi flow is found from the throat area, the discharge coefficient, the beta ratio velocity correction and the square root of differential pressure.
Q = Cd x A2 / sqrt(1 - beta^4) x sqrt(2 x dP / rho)
At a glance
| What it does | Airflow from a venturi meter's throat differential pressure. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Inlet pipe diameter, Throat diameter, Differential pressure, Discharge coefficient, Air density |
| Main output | Airflow |
| Formula | Q = Cd x A2 / sqrt(1 - beta^4) x sqrt(2 x dP / rho) |
| Cost | Free — no sign-up, no download |
How to use the Venturi Flow Calculator
- 1Enter the inlet and throat diameters of the venturi, the differential pressure and air density.
- 2The tool applies the beta-ratio correction for the velocity of approach.
- 3Use the manufacturer's calibrated discharge coefficient when available for best accuracy.
Inputs explained
- Inlet pipe diameter(in)
- Enter the inlet pipe diameter in in.
- Throat diameter(in)
- Enter the throat diameter in in.
- Differential pressure(in wc)
- Enter the differential pressure in in wc.
- Discharge coefficient
- Enter the discharge coefficient you are working with.
- Air density(lb/ft3)
- Enter the air density in lb/ft3.
Worked example
Using the values the calculator loads with:
Inputs
- Inlet pipe diameter10 in
- Throat diameter6 in
- Differential pressure3.0 in wc
- Discharge coefficient0.98
- Air density0.075 lb/ft3
Results
- Airflow252 CFM
- Throat velocity21.4 ft/s
- Beta ratio0.6
Frequently asked questions
Why correct for beta ratio?
The upstream velocity is not negligible, so the simple orifice equation must be corrected for the area contraction ratio.
Venturi vs orifice plate?
Venturis have much lower permanent pressure loss and a higher discharge coefficient close to 1.
What do I need to enter into the Venturi Flow Calculator?
Just 5 values: inlet pipe diameter, throat diameter, differential pressure, discharge coefficient, air density. 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 Venturi Flow Calculator work out the answer?
Venturi flow is found from the throat area, the discharge coefficient, the beta ratio velocity correction and the square root of differential pressure. It applies the formula Q = Cd x A2 / sqrt(1 - beta^4) x sqrt(2 x dP / rho) and shows the working so you can check each step by hand.
Is the Venturi Flow 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.