Orifice Plate Flow Calculator
Airflow from an orifice plate differential pressure reading.
Enter your values
Enter the orifice 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
- 53 CFM
- Orifice velocity
- 10.2 ft/s
- Orifice area
- 0.0873 sq ft
Quick answer
Flow through an orifice plate is proportional to the discharge coefficient, orifice area and the square root of the differential pressure.
Q = C x A x sqrt(2 x dP / rho)
At a glance
| What it does | Airflow from an orifice plate differential pressure reading. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Orifice diameter, Differential pressure, Discharge coefficient, Air density |
| Main output | Airflow |
| Formula | Q = C x A x sqrt(2 x dP / rho) |
| Cost | Free — no sign-up, no download |
How to use the Orifice Plate Flow Calculator
- 1Enter the orifice bore diameter, discharge coefficient (typically 0.6-0.62 for sharp-edged plates) and measured differential pressure.
- 2The tool converts pressure to velocity through the orifice and multiplies by area.
- 3Confirm the coefficient against the plate manufacturer's calibration for best accuracy.
Inputs explained
- Orifice diameter(in)
- Enter the orifice 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
- Orifice diameter4 in
- Differential pressure2.0 in wc
- Discharge coefficient0.61
- Air density0.075 lb/ft3
Results
- Airflow53 CFM
- Orifice velocity10.2 ft/s
- Orifice area0.0873 sq ft
Frequently asked questions
Where is Cd from?
Sharp-edged concentric orifice plates typically use 0.60-0.62; use the manufacturer's calibrated value if available.
Does beta ratio matter?
Yes for precise metering; this calculator assumes a simple orifice-in-duct approximation.
What do I need to enter into the Orifice Plate Flow Calculator?
Just 4 values: orifice 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 Orifice Plate Flow Calculator work out the answer?
Flow through an orifice plate is proportional to the discharge coefficient, orifice area and the square root of the differential pressure. It applies the formula Q = C x A x sqrt(2 x dP / rho) and shows the working so you can check each step by hand.
Is the Orifice Plate 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.