Pipe diameter and flow rate calculator

round, closed, full pipe diameter calculation

online since 2007

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Calculation setup
Flow rates and velocity
Pipe dimensions
Fluid properties

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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 - pipe diameter
Internal circular pipe diameter
V - velocity
Flow velocity in terms of units of distance per unit of time
A - area
Internal pipe cross section area
ρ - fluid density
Mass per unit of volume
T - temperature
Fluid temperature for gas density calculation based on the ideal gas state equation
p - pressure
Fluid pressure at the start of the pipe 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

Calculation setup

Select value to calculate. You should enter not selected one.
pipe diameter
flow velocity
Select value to input. You should enter selected one. The other one will be calculated
volumetric flow rate
mass flow rate
Select value to input. You should enter selected one. The other one will be calculated. Available only if the gas is selected fluid
fluid density
Select fluid type
for incompressible fluids
for fluids where ideal gas state equation is used. Enables selection between density and temperature to input.
Select pipe shape
round pipe
full cross section fluid flow
rectangle pipe
for rectangle channels and full cross section flow

When is this calculator applicable?

Calculation of pipe diameter with the pipe diameter calculator is easy. You can use pipe diameter and flow rate calculator for quick pipe diameter calculation in a closed, round, rectangle (online calculator version only) and filled pipes with liquid or perfect gas.

For a calculation of the pipe diameter with this calculator, you should know and enter the flow velocity. It the flow velocity is unknown then you have to use the pressure drop calculator to calculate pipe diameter. You can use pressure drop calculator when the pressure difference between the start and the end of the pipeline (head loss) is available as a known value.

With pipe diameter calculator pipe internal diameter is calculated using the simple relation between flow rate, velocity and cross-section area (Q=v·A).

To calculate internal pipe diameter, you should only enter flow rate and velocity in corresponding fields in the calculator and click calculate button to get results.

Other values, besides internal pipe diameter, can be calculated as well. You can calculate flow velocity for the given fluid flow rate and internal pipe diameter. As velocity is different on different places of pipe cross-section area, flow mean velocity is computed based on the continuity equation.

The flow rate used in calculator can be mass or volume flow rate.

Conversion between mass and volume flow rate is available for given fluid density. Also, for perfect gases, volume flow rate conversion for different flow conditions (pressures and temperatures) is possible, so you can quickly calculate the volume flow rate on specific pressure or specific temperature in the pipe, like after pressure reducing valves.

If flowing fluid is perfect gas, you can calculate volume flow rate of that gas at different pressures and temperatures. For example, if you know volume flow rate of some ideal gas at some predefined pressure and temperature (like at normal conditions p=101325 Pa and T=273.15 K), you can calculate actual volume flow rate for pressure and temperature that is actually in the pipe (for example, the real pressure and temperature in the pipeline is p=30 psi and t=70 F). Volume flow rate of the perfect gas is different at these two conditions. Read more about normal conditions for pressure and temperature.

With this calculator, you can convert volume flow rate from standard or some other predefined conditions to actual conditions and vice versa. The calculator uses the mass conservation law for computation of volume flow rates for this two conditions, meaning that mass flow is constant, despite that conditions, like pressure and temperature are changing.

The mass conservation law is applicable only if the stream is in the closed pipe, without added or subtracted flow, if the flow is not changing in time and a few other conditions. Read more about mass conservation of mass.

So when it is not applicable?

This calculator has an almost limitless application, but some functionalities are dependent on several conditions.

As mentioned above, pipe diameter calculation with this calculator is not possible if you are not sure about flow velocity and volume/mass flow rate. If any of these two are missing, then you should use pressure drop calculator.

You have to know the density of the liquid if the mass flow rate is available instead of the volume flow rate. If the density of the liquid is unavailable, and only the mass flow rate is known, then the volume flow rate required for pipe diameter calculation is not possible.

For perfect gases, the density of the fluid is not mandatory, if you know the pressure, temperature and gas constant for the flowing gas. The calculator uses the perfect gas equation for density calculation. However, if the flowing fluid is gas but not a perfect (ideal) gas, i.e., if it's pressure, temperature and density are not related according to ideal gas law, this calculator is not applicable if you are trying to calculate that gas density for known pressure and temperature.

What has to be known to calculate pipe diameter?

To calculate pipe diameter, you have to know flow velocity and flow rate. If you know mass flow rate, then fluid density has to be known.

If the flowing fluid is gas, then instead of density, you have to know gas constant, absolute pressure, and temperature. Density is calculated using the equation for the perfect gas.

What has to be known to calculate flow velocity?

To calculate flow velocity, you have to know flow rate and pipe interior diameter. If you know mass flow rate, then fluid density has to be known.

If the flowing fluid is gas, then instead of density, you have to know gas constant, absolute pressure, and temperature. Density is calculated using the equation for the perfect gas.

How is the calculation performed?

Pipe diameter and flow velocity calculation use the continuity equation that gives the relation between flow rate, flow velocity, and interior pipe diameter.

For gas flow, the equation for perfect gas is used to calculate density from gas constant, absolute pressure, and temperature.

Available in download version

save/open multiple results
export to word and excel
print results
custom fluid properties
K factor for fittings, resistance coefficient
pipe surface roughness selection
select between gauge and absolute pressure
compressible isothermal flow
dry air isothermal flow
gas offtake flow
natural gas flow


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Issues and answers

Having problems with calculators usage? Read more about known issues and problems and way to solve it.

Issues and answers

Watch how calculator can help you resolve task in less than a minute

PipDiaWaterQ, vD

Example #1

Task: Calculate the pipe diameter if the water flow velocity is 1 m/s and the flow rate is 5 lit/min.

Solution: Pipe diameter is 10.3 mm

PipDiaAirQ, Dv

Example #2

Task: Calculate the airflow velocity if the inner diameter of the pipe is 50 mm and the flow rate is 100 m3/h at a pressure of 3 bar absolute and a temperature of 15 °C

Solution: Flow velocity is 14.15 m/s

PipDiaCarbon dioxideQ, vD

Example #3

Task: Calculate the diameter of the carbon dioxide pipe with a flow rate of 10 kg/h and a velocity 2 m/s at a pressure of 7 bar absolute and a temperature of 20 °C.

Solution: Pipe diameter is 11.8 mm

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