Orifice plate is very practical and relatively low-cost measuring device for flow rate measurement with good accuracy. By placing orifice plate in the pipe, sudden pressure drop is created. Degree of created pressure drop is directly proportional to the stream velocity and consequently, to the flow rate. That behavior and strong interaction between stream velocity and pressure drop due to local restrictions is used for flow rate measurement by orifice plate.

This calculator can be used for calculating of actual flow rate through orifice plate flow meter, for measured pressure drop and can also be used for orifice plate sizing.

- Flow rate for known orifice size and pressure difference
- Flow velocity in the inlet pipe
- Discharge coefficient calculation
- Gas expansion coefficient for compressible flow

In Selection section you can select values to input. Not selected values will be calculated. You select between:

- flowing fluid - gas or liquid
- pressure after the orifice or pressure difference in front and after the orifice
- kinematic or dynamic viscosity
- density or temperature for gases
- orifice tap position type
- calculation within or out of ISO5167 constraints

In Report section you have instant calculation report for input values. From there you can copy/paste report to your text editor.

- Conversion between volumetric and mass flow rate
- Calculation of Reynolds number included
- Applicable for non-compressible liquids and compressible perfect gases
- For pressure measuring position in terms of corner taps, 1 inch taps and also D and D/2 taps
- For single-phase fluid, subsonic, non-pulsating flow
- ISO 5167 based calculation

- q - volumetric flow rate
- Fluid flow rate in terms of units of volume per unit of time
- ṁ - mass flow rate
- Fluid flow rate in terms of units of mass per unit of time
- D
_{1}- diameter of tube - Internal pipe diameter
- D
_{2}- orifice diameter - Diameter of orifice
- V
_{1}- upstream velocity - Flow velocity in front of the orifice where flow diameter is D
_{1} - V
_{2}- orifice velocity - Flow velocity in the orifice where flow diameter is D
_{2} - A - area
- Internal pipe cross section area
- ρ - fluid upstream density
- Density of fluid in front of orifice in terms of mass per unit of volume
- ν - kinematic viscosity
- Result of fluid particles colliding to each other and moving at different velocities in terms of area per square unit of time
- μ - dynamic viscosity
- Result of fluid particles colliding to each other and moving at different velocities in terms of mass per square unit of distance and time
- κ- isentropic coefficient
- Specific heat ratio
- e - expansion factor
- Coefficient used for compressible flow calculation
- C - coefficient of discharge
- Coefficient used for orifice plate based on ISO 5167
- R
_{eD}- upstream Reynolds number - Reynolds number calculated in front of the orifice
- p
_{1}- pressure on the inlet - Absolute pressure in front of the orifice
- p
_{2}- pressure on the outlet - Absolute pressure after the orifice
- p
_{1}- p_{2}- pressure drop - Pressure difference between pipe start and pipe end
- T - temperature
- Fluid temperature for gas density calculation based on the ideal gas state equation
- R - gas constant
- Gas constant in terms of energy per unit of mass and temperature, for gas density calculation using ideal gas state equation

- Related links:
- Orifice plates on Wikipedia.
- ISO 5167-2 standard for orifice plate measurement.
- Adiabatic process text on Wikipedia.