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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

- Select value to calculate. You should enter not selected one.
- D
- pipe diameter
- V
- flow velocity

- Select value to input. You should enter selected one. The other one will be calculated
- q
- volumetric flow rate
- ṁ
- 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
- ρ
- fluid density
- T
- temperature

- Select fluid type
- liquid
- for incompressible fluids
- gas
- 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

PipDiaWaterQ, vD

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

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

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