Just Wait...


Calculates flow or velocity and pressure drop through a circular or rectangular duct.

Circular duct

Input Result
Flow q=
Duct diameter d=
Velocity v=
Kinetic viscosity ν= *10-6 m2/s
Density ρ=
Material roughness k=
Pressure drop Δp=

Rectangular duct

Input Result
Flow q=
Height a=
Width b=
Kinetic viscosity ν= *10-6 m2/s
Density ρ=
Material roughness k=
Velocity v=
Pressure drop Δp=
Equivalent circular diameter de=



The airflow in the estimated circular canal.

Duct diameter

The actual circular duct diameter. The diameters that are selectable are the usual standard diameters available.

Kinematic viscosity

Specifies how quickly a liquid spreads relative to its mass if it is poured out on a flat surface. In the original case, the viscosity inematiska sat by air at 20˚C.

Dynamic viscosity

Are proportionality factor for the force it takes to parallel displace a surface relative to another, if the gap between these surfaces is filled with a viscous liquid or gas.


Density or volume of the mass is an SI unit and is a measure of a specific substance density, ie mass per unit volume. A synonym for density that can sometimes occur is specific gravity. In the original case, the density is set to air at 20c.


The width of the current rectangular duct.


The height of the current rectangular duct.

Equivalent circular diameter

Shows how much a matched sensed circular duct would need to be to achieve the same values ​​as the current rectangular.


Pipe pressure drop corresponds to the force required to move the medium in the relevant pipe of 1 meter.

Speed ​​

the velocity of the medium in the tube.

Material roughness

A material constant that indicates how the material is smooth duct.


Flow: Flow
Hagen-Poiseuille: Hagen-Poiseuille Pressure drop for laminar flow.
Darcy-Weisbach: Darcy-Weisbach Pressure drop for turbulent flow.
Colebrook-White: Colebrook-White
Serghides: Serghides Approximate solution to Colebrook-White
Serghides part 1
Serghides part 2
Serghides part 3
Reynolds number: Reynolds number
Hydraulic diameter: Hydraulic diameter
Dynamic viskosity: Dynamic viskosity
Equivalent circular diameter: Equivalent circular diameter