Calculate Flow Through an Orifice Plate
Use SI units. This calculator estimates volumetric and mass flow rate using a standard incompressible-flow orifice equation.
What is an orifice meter?
An orifice meter is a differential-pressure flow meter used in water systems, chemical plants, HVAC, steam lines, and process industries. It uses a flat plate with a circular hole (the orifice) installed in a pipe. As fluid passes through the constriction, velocity increases and pressure drops. By measuring that pressure drop, flow rate can be estimated.
Equation used in this orifice meter calculator
This tool uses a common incompressible-flow form of the orifice equation:
- Q = volumetric flow rate (m³/s)
- Cd = discharge coefficient
- ε = expansibility factor
- Ao = orifice area = πd²/4
- ΔP = differential pressure (Pa)
- ρ = fluid density (kg/m³)
- β = diameter ratio = d/D
When this model works well
It is best for steady, single-phase flow where density is known and installation follows good piping practice. For high-compressibility gas flow, wet gas, pulsating flow, or poor upstream conditions, use full standards-based methods (such as ISO 5167) and site calibration data.
How to use the calculator
- Enter the pipe diameter and orifice diameter in mm.
- Enter measured differential pressure across the orifice in kPa.
- Enter fluid density in kg/m³.
- Set Cd (0.61 is a common starting point for sharp-edged plates).
- Keep ε = 1 for liquids; use a gas-specific value when appropriate.
- Optionally enter viscosity to estimate Reynolds number.
Sample interpretation of results
The calculator returns:
- Volumetric flow in m³/s, m³/h, and L/s
- Mass flow rate in kg/s
- β ratio and flow velocities in pipe/orifice
- Equivalent head loss from the measured differential pressure
- Reynolds number if viscosity is provided
Accuracy considerations
1) Discharge coefficient uncertainty
Cd is not a universal constant. It varies with Reynolds number, plate edge condition, tapping configuration, and upstream disturbances.
2) Density and temperature
Density can change with temperature and composition. If density is off by 2%, flow can be off noticeably as well.
3) Pressure transmitter quality
Because flow depends on the square root of differential pressure, low-range transmitter errors can still create meaningful uncertainty in calculated flow.
4) Installation effects
Swirl, elbows too close to the plate, poor straight-run lengths, and damaged plate edges all reduce reliability. Proper meter run design matters.
FAQ
Can I use this for steam or natural gas?
Yes as a quick estimate, but you should include compressibility/expansion effects and standards-based corrections for engineering-grade reporting.
What is a typical discharge coefficient?
For sharp-edged concentric plates, 0.60 to 0.62 is often used as a starting range. Final values should come from standard methods and measured conditions.
Why does higher ΔP increase flow?
Because available pressure energy drives acceleration through the restriction. Flow scales roughly with the square root of ΔP, not linearly.