Pipe Diameter And Flow Rate Calculator, Online

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This pipe size calculator determines the required pipe diameter based on flow rate and flow velocity. It is used for pipe sizing calculations in liquid and gas flow systems. Use the calculator below to perform accurate pipe size and pipe diameter calculations.

Pipe diameter directly influences flow velocity and the Reynolds number. To determine whether the flow is laminar or turbulent, use the Reynolds Number Calculator.

After selecting the pipe diameter, the resulting pressure loss can be evaluated using the Pressure Drop Calculator.

Calculate Flow Velocity, Pipe Size, and Flow Rate for Liquids and Gases

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Pipe diameter calculator

Easily calculate pipe diameter and flow rate using the continuity equation. Our pipe flow calculator helps determine the correct pipe size based on volumetric flow rate and velocity, making it ideal for both liquid and gas flow applications.

Suitable for engineering, HVAC, plumbing, and fluid dynamics.

How Does the Pipe Diameter And Flow Rate Calculator Works?

The calculator applies the continuity equation.

The continuity equation is a fundamental principle in fluid mechanics based on the conservation of mass. It states that for an incompressible fluid (constant density), the mass flow rate remains constant along a streamline. The equation is:

Q = A ⋅ V

Where:

• 𝑄 = Volumetric flow rate (m³/s)
• 𝐴 = Cross-sectional area of the pipe (m²)
• 𝑉 = velocity (m/s)

Since the cross-sectional area of a circular pipe is:

A = π D 2 4

We can rewrite the equation as:

Q = π D 2 4 ⋅ V

Solving for Pipe Diameter (D):

D = 4 ⋅ Q π ⋅ V

where:

• D = internal pipe diameter (m)
• Q = volume flow rate
• V = velocity (m/s)

Mass Flow Rate vs. Volume Flow Rate: Formula and Conversion Guide

The relationship between mass flow rate (m) and volume flow rate (Q) is given by:

m ˙ = ρ ⋅ Q

Solving for Q:

Q = m ˙ ρ

The density (ρ) of a perfect gas is given by the perfect gas law, in the next chapter.

Perfect Gas Density Formula: How to Calculate Gas Density Using Pressure and Temperature

The density (ρ) of a perfect gas is given by the ideal gas law:

ρ = P R ⋅ T

where:

• ρ = Gas density (kg/m³)
• P = Absolute pressure (Pa)
• T = Absolute temperature (K)
• R = Specific gas constant (J/kg·K), defined as 𝑅=𝑅𝑢/𝑀, where 𝑅𝑢 is the universal gas constant and M is the molar mass of the gas.

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Imperial units Metric units Export Word Export Excel Results Save Load Calculate for: Select values to input: Flow rates and velocityVolume flow rate (q) m³/s m³/min m³/hour l/s l/min l/hour ft³/s ft³/min ft³/hour in³/s in³/min yd³/min gps UK gpm UK gph UK gps US gpm US gph US Mass flow rate (ṁ) kg/s kg/min kg/hour g/s g/min g/hour slug/s slug/min slug/hour lbm/s lbm/min lbm/hour oz/s oz/min oz/hour Velocity (V) m/s m/min m/hour km/s km/min km/hour ft/s ft/min yd/s mph Pipe dimensions Pipe diameter (D) cm mm ft in Cross section area (A) mm² cm² m² in² ft² yd² Fluid properties Density (ρ) kg/m³ kg/l g/l g/cm³ lbm/in³ lbm/ft³ lbm/yd³ lbm/gal US lbm/gal UK oz/in³ oz/ft³ slug/in³ slug/ft³ slug/yd³

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Description

q - volumetric flow rateFluid flow rate in terms of units of volume per unit of time ṁ - mass flow rateFluid flow rate in terms of units of mass per unit of time D - pipe diameterInternal circular pipe diameter V - velocityFlow velocity in terms of units of distance per unit of time A - areaInternal pipe cross section area ρ - fluid densityMass per unit of volume T - temperatureFluid temperature for gas density calculation based on the ideal gas state equation p - pressureFluid pressure at the start of the pipe for gas density calculation based on the ideal gas state equation R - gas constantGas constant in terms of energy per unit of mass and temperature, for gas density calculation using ideal gas state equation

Calculation Setup

Use this guide to correctly configure the parameters required for calculating pipe diameter, flow velocity, and flow rates. The calculator automatically computes any non-selected variable based on your input and selected fluid type.

Select the value you want the calculator to compute. The selected variable should not be entered manually. D Pipe diameter required for the specified flow. V Flow velocity inside the pipe. Choose which flow rate you want to input. Enter only the selected one; the other will be calculated automatically. q Volumetric flow rate. ṁ Mass flow rate. Choose which property to enter. The other value will be calculated automatically. This option is available only when the selected fluid is a gas. ρ Fluid density. T Fluid temperature. Select the fluid type used in the calculation. liquid For incompressible fluids where density remains constant. gas For compressible fluids where the ideal gas equation is used. Enables choosing whether density or temperature will be entered. Select the pipe shape. round pipe Standard circular pipe with full cross-section flow. rectangular duct For rectangular channels with full cross-section fluid flow.

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When is This Flow Rate Calculator Applicable?

Using a pipe diameter and flow rate calculator makes it easy to determine pipe diameter, flow rate or velocity in the pipe. Our pipe diameter and flow rate calculator allows quick calculations for closed, round, and rectangular pipes, filled with liquid or a perfect gas.

If you're analyzing a system with multiple pipes, consider using a pipe network analysis calculator.

For accurate pipe diameter calculation, you must enter the flow velocity. If flow velocity is unknown, use the pressure drop calculator to determine flow rare or pipe diameter based on the pressure difference (head loss) between the pipeline's start and end.

How Does the Pipe Diameter and Flow Rate Calculator Work?

The pipe diameter calculator determines internal pipe diameter using the fundamental relation between flow rate, velocity, and cross-sectional area (Q = v·A).

To calculate pipe diameter

• Enter the flow rate and velocity in the calculator.
• Click the calculate button to get results.

To calculate flow rate

• Enter the pipe diameter and velocity in the calculator.
• Click the calculate button to get results.

To calculate flow velocity

Besides pipe diameter, the calculator can also determine:

• Flow velocity for a given flow rate and internal pipe diameter.
• Mass or volume flow rate conversions, using fluid density.

If working with perfect gases, you can convert volume flow rate based on pressure and temperature changes. This is useful for pipelines with pressure-reducing valves or varying conditions.

For example, if you know the volume flow rate of an ideal gas at standard conditions (p = 101325 Pa, T = 273.15 K), you can calculate its actual volume flow rate at real pipeline conditions, like p = 30 psi and t = 70°F.

When is the Flow Rate Calculator Not Applicable?

Although highly versatile, some limitations exist:

• If flow velocity and flow rate are both unknown, use a pressure drop calculator instead.
• For mass flow rate calculations, fluid density must be known. If density is unknown, mass flow rate calculations are not possible.
• For gases, if pressure, temperature, and density do not follow the ideal gas law, the calculator cannot determine gas density.

What Information is Needed for Calculations?

• To calculate pipe diameter, you must know flow velocity and flow rate. If using mass flow rate, fluid density must be known.
• For gas flow, density is derived from gas constant, absolute pressure, and temperature using the perfect gas equation.
• To calculate flow velocity, the required inputs are flow rate and pipe interior diameter.

How is the Calculation Performed?

The flow rate calculator uses the continuity equation to relate flow rate, flow velocity, and pipe diameter.

For gas flow, the ideal gas equation determines density based on gas constant, absolute pressure, and temperature.

This flow rate calculator is an essential tool for engineers and professionals working with liquid and gas pipelines. Whether determining pipe diameter, flow velocity, or flow rate conversions, it simplifies complex calculations efficiently.

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Features in desktop app

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• Gas offtake flow
• Natural gas flow
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Related links

• Read more on Continuity equation
• Look at Conservation of mass
• Find more about Standard conditions of gases.