" Orifice Plate Calculator – Flow and Diameter Calculation

Orifice Plate Calculator for Flow Rate and Sizing Calculation

This orifice plate calculator is used to perform flow rate and orifice sizing calculations based on the measured pressure drop. The calculation follows standard orifice flow equations commonly used in flow measurement and fluid mechanics. Use the calculator below for accurate orifice plate and flow calculation in piping systems.

Orifice plate sizing and flow rate calculation

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Flow Rate Calculation for Fluids Through an Orifice or Nozzle

The flow rate of a fluid passing through an orifice or nozzle can be determined using the following equation:

Fluid Flow Through an Orifice or Nozzle

$q = \frac{C_{d} \cdot A}{\sqrt{1 - β^{4}}} \cdot \sqrt{2 \cdot g_{n} \cdot h_{L}}$

Where:

q = Flow rate
C_d = Coefficient of discharge
A = Cross-sectional area
β = Diameter ratio (d₁/d₂)
gₙ = Acceleration due to gravity
hL = Head loss

Instead of using the coefficient of discharge (Cd), a more practical approach is to apply the flow coefficient (C), which is defined as:

Flow Coefficient Formula

$C = \frac{C_{d}}{\sqrt{1 - β^{4}}}$

$q = C \cdot A \cdot \sqrt{2 \cdot g_{n} \cdot h_{L}}$

Where:

C = Flow coefficient
C_d = Coefficient of discharge
β = Diameter ratio (d₁/d₂)

By utilizing the flow coefficient, engineers and fluid mechanics professionals can achieve more accurate calculations for fluid dynamics, hydraulic systems, and nozzle flow efficiency.

Coefficient of Discharge for Orifice Flow (ISO 5167)

The coefficient of discharge (Cd) for orifice flow can be determined using the Reader-Harris/Gallagher (1998) equation as specified in ISO 5167:

Coefficient of Discharge Formula

Where:

β = Diameter ratio (d₁/d₂)
R_eD = Reynolds number based on the larger diameter
d₁ = Smaller internal diameter
d₂ = Larger internal diameter

Tap Configurations and Coefficient Adjustments

The values of L₁ and L₂ depend on the type of pressure tap used:

Corner taps: L₁ = L₂ = 0
D and D/2 taps: L₁ = 1, L₂ = 0.47
1-inch taps: L₁ = L₂ = 0.0254/d₁ (for d₁ in meters)

By applying these fluid flow equations, engineers can enhance flow measurement accuracy in hydraulic systems, pipelines, and industrial fluid applications.

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Pressures

absolute pressure in front of the orifice (p1)

absolute pressure after the orifice (p2)

measured pressure difference (Δp)

pressure loss (Δω)

Flow rates and velocities

volume flow rate (q1)

volume flow rate at standard cond. (q)

mass flow rate (ṁ)

velocity in pipe (V1)

Orifice dimensions and coefficients

pipe internal diameter (D1)

orifice diameter (D2)

expansion factor (e)

coefficient of discharge (C)

Reynolds number in pipe (Re)

resistance coefficient (K)

Fluid properties

temperature in front of the orifice (T1)

inlet density (ρ1)

gas constant (R)

isentropic coefficient (κ)

kinematic viscosity (ν)

dynamic viscosity (μ)

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Description

p₁ - pressure on the inlet: Absolute pressure in front of the orifice
p₂ - pressure on the outlet: Absolute pressure after the orifice
Δp - pressure drop: Pressure difference between pipe start and pipe end
Δω - pressure loss: That can't be recovered after the orifice
D₁ - diameter of tube: Internal pipe diameter
D₂ - orifice size: Diameter of orifice
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
K - resistance coefficient: That you can use in pipeline calculation, as orifice is creating local pressure losses in the pipeline
q₁ - volumetric flow rate: Fluid flow rate in terms of units of volume per unit of time on the inlet conditions
q - standard flow: Flow rate at standard conditions. Used only if the selected fluid is gas.
ṁ - mass flow rate: Fluid flow rate in terms of units of mass per unit of time
V₁ - upstream velocity: Flow velocity in front of the orifice where flow diameter is D₁
T₁ - upstream temperature: Fluid temperature for gas density calculation based on the ideal gas state equation
ρ₁ - upstream density: Fluid density in the front of orifice in terms of mass per unit of volume
R - gas constant: Gas constant in terms of energy per unit of mass and temperature, for gas density calculation using ideal gas state equation
κ - isentropic coefficient: Specific heat ratio
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

Sizing calculation setup

Select orifice type based on the measuring taps placement
Corner taps: When measuring taps are placed in the orifice corners
Flange taps: When measuring taps are placed in the orifice flanges
D - D/2: When measuring taps are placed in front and after the orifice on given distance

Select value to input. You should enter selected one. The other one will be calculated
p₂: pressure downstream from the orifice
Δp: measured pressure difference in front and after the orifice

Select value to input. You should enter selected one. The other one will be calculated
ν: kinematic viscosity
μ: dynamic viscosity

Select value to input. Available only if gas is selected. You should enter selected one. The other one will be calculated
T₁: upstream temperature.
ρ₁: upstream density.

Select fluid type
Gas: for compressible flow where ideal gas state equation is applicable
Liquid: for incompressible flow of liquids

Application of ISO 5167 constraints
ISO constraints: Deselect if you don't want to check if the orifice and the flow conditions are within the limits of the ISO standard.

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Why Use This Orifice Sizing Calculator?

Our orifice sizing calculator quickly determines the actual flow rate through an orifice plate flow meter using just a few inputs. By measuring the pressure drop caused by the orifice plate in the pipeline, this tool provides precise flow calculations for engineers and technicians.

When Should You Use This Calculator?

Liquids and perfect gases
Subsonic, single-phase fluid flow
Circular pipelines

Not suitable for: Pulsating flows, rectangular ducts, or non-ideal gases.

When Is This Calculator Not Applicable?

This tool does not support:

Multiphase flows (e.g., liquid with solid particles or undissolved gases)
Non-ideal gas flows (gases that don’t follow the ideal gas law)

What Inputs Are Required for Orifice Flow Calculation?

To perform a precise orifice plate flow rate calculation, enter the following:

Throat diameter of the orifice plate
Pipe interior diameter
Fluid properties – Density and viscosity (for liquids)
Gas properties – Gas constant, pressure, and temperature (for gases)

For gas flow calculations, density is automatically computed using the perfect gas equation based on real conditions.

How Does This Orifice Plate Calculator Work?

The calculation follows ISO 5167-2 standards to ensure accuracy. Reliable results are only achieved if the orifice plate design meets these criteria.

ISO 5167-2 Orifice Plate Flow Conditions

For Corner, D, and D/2 Pressure Tappings:

Orifice diameter (d) > 12.5 mm
Pipe diameter (D) between 50 mm and 1000 mm
Beta ratio (β) between 0.1 and 0.75
Reynolds number (ReD) > 5000 (if β < 0.56)
Reynolds number (ReD) > 16000 × β² (if β > 0.56)

For Flange Pressure Tappings:

d > 12.5 mm
D between 50 mm and 1000 mm
β between 0.1 and 0.75
ReD > 5000 and ReD > 170 × β² × D

What Happens If These Conditions Aren’t Met?

If the orifice plate or flow conditions do not comply with ISO 5167-2, the calculator will display a warning message. However, you can choose to bypass ISO constraints and proceed with the calculation at your own discretion.

Try the Orifice Sizing Calculator Now!

Get fast, accurate orifice flow rate calculations using our easy-to-use tool. Perfect for engineers, fluid mechanics specialists, and industrial applications!

Features in desktop app

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Export to Word and Excel
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Create list of custom fluid properties
Resistance factor K for valves/fittings
Pipe surface roughness selection
Pipe material selection
Gauge vs absolute pressure toggle
Compressible isothermal flow
Dry air isothermal flow
Gas offtake flow
Natural gas flow
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Orifice Plate Calculator for Flow Rate and Sizing Calculation

Orifice plate sizing and flow rate calculation

Online Calculator

Desktop App

Flow Rate Calculation for Fluids Through an Orifice or Nozzle

Coefficient of Discharge for Orifice Flow (ISO 5167)

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Description

Sizing calculation setup

Why Use This Orifice Sizing Calculator?

When Should You Use This Calculator?

When Is This Calculator Not Applicable?

What Inputs Are Required for Orifice Flow Calculation?

How Does This Orifice Plate Calculator Work?

ISO 5167-2 Orifice Plate Flow Conditions

For Corner, D, and D/2 Pressure Tappings:

For Flange Pressure Tappings:

What Happens If These Conditions Aren’t Met?

Try the Orifice Sizing Calculator Now!

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