Pipe flow calculators

Pipe diameter calculator

Calculator Description

This calculator can be used for the calculation of internal pipe diameter and cross section area for a known flow rate of either liquid fluid or gas, including flow velocity calculation.

  • Calculate:

    • Pipe diameter
    • Flow velocity
  • Input:

    • Pressure of gas
    • Fluid density of gas
    • Temperature of gas
    • Flow rate
    • Weight flow rate

Calculator Features

  • Continuity equation based
  • Suitable for both, liquids and gases
  • Capability to convert between volumetric and mass flow rate
  • Calculation of actual volumetric flow rate for particular pressure and temperature

This is a highly practical and reliable calculator which can be simply used for calculating the pipe size for provided volumetric or weight flow rate and stream velocity. Alternatively, you can also use it for calculating velocity for known pipe size and rate of flow. In addition, it is also possible for the user to calculate both, weight or volumetric flow rate and convert between them.

Calculation is based on the continuity equation. It is general equation and suitable for all fluids, so you can use calculator for incompressible liquids and compressible gases.

In the case that flowing fluid is perfect gas, you can calculate the flow amount at different temperatures and pressures using the fact that the amount of weight flow is constant, despite pressure and temperature change.

If, in your case, the weight or volumetric flow rate is unknown and you want to calculate pipe diameter, than this calculator will not work for you. In that case, you should use a calculator for pressure drop calculation.

Finally, since the fluid velocity along a cross section area differs in various places of pipe, flow mean velocity across pipe section area is used in calculation. Mean velocity is calculated based on the continuity equation.

Please tell me what do you think about this calculator

If you would like to use the calculator, but actually can't see the blue CALCULATOR button in the upper left part of the page than please read instructions.

Q: Calculate internal pipe diameter for 2 l/s of water flow with flow velocity of 2 m/s.

A: Calculation setup:
Calculate for: liquid
Input one from following two:
q - volumetric flow rate
v - velocity
Enter values:
q = 2 l/s
v = 2 m/s
rho = 1000 kg/m3

Q: Calculate air flow velocity in closed round pipe with internal diameter of 450 mm, weight flow rate of 10000 kg/h at 50 mbar gauge pressure, temperature of 20 OC.

A: Calculation setup:
Calculate for: gas
Input one from following two:
w - weight flow rate
T - temperature
D - diameter
Enter values:
w = 10000 kg/h
d = 450 mm
p = 1063 mbar (absolute)
T = 20 OC
R = 287 J/kgK

Q: Calculate flow rate on normal conditions (p=101325 Pa and T=0 OC) if measured flow on actual pressure of 6 barg and temperature of 10 OC is 10000 m3/h.

A: Calculation setup:
Calculate for: gas
Input one from following two:
q - volume flow rate
T - temperature
D - diameter (irrelevant)
At first enter values:
Q = 10000 m3/h
p = 7013 mbar (absolute)
T = 10OC
R = 287 kJ/kgK
After w is calculated switch to:
Input one from following two:
w - weight flow rate
Keeping calculated w constant change pressure and temperature to normal conditions:
p = 1013 mbar
T = 0OC
and you will have calculated volumetric flow rate q - at normal conditions.

Equation used for pipe diameter calculation

Read more about used theory on pipe flow theory page.

If you experience problems with calculator start try to find answers on instructions page.

Have a question about the site or calculators? Try to find the answer immediately on forum.