Pipe flow calculators

Gas discharge calculator


Calculator Description

Gas pipe outflow calculator can be used for flow rate or pipe diameter calculation where gas flows out from pipe or reservoir to atmosphere or other pipe or reservoir. It can be used for all two and three atomic perfect gases including air, nitrogen, carbon dioxide and others. Calculator can be used for flow through pipes with or without valves and fittings in the pipe line.

  • Calculate:

    • Outflow weight flow rate
    • Gas expansion factor
    • Flow velocities
    • Friction factor
    • Reynolds number
  • Input:

    • Internal pipe diameter
    • Pressure drop
    • Gas properties
    • Pipeline length
    • Local resistance coefficient K
    • Pipe surface roughness

Calculator Features

  • For all two and three atomic gases
  • For pipes with or without valves and fittings
  • Chocked flow conditions checked and presented

With gas discharge calculator you can calculate maximum flow rate for known pressure difference and pipe diameter, or you can calculate pipe diameter for known flow rate and pressure drop. Based on the known pressure difference (head loss) between one point of flow stream at the start of pipe or in front of the valve, to the outside point (like atmosphere), or after the valve with known inside pipe diameter, weight flow rate and volume flow rate is calculated. Calculator is for steady flow with constant pressures in one point of stream line.

Calculator is checking if flow is choked or not and choked flow status is presented and flow rate is calculated at choked conditions.


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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 flow rate of air flowing through 2 m long pipe to open atmoshere with 20 mm inside diameter. Pipe internal roghness is 0.1 mm and local resistance coefficient is K = 1.5. Air temperature is 288 K. On the pipe start, air is under 150000 Pa absolute pressure.

A: Calculation setup:
Input values:
D = 20 mm
p1 = 150000 Pa
p2 = 101325 Pa
L = 2 m
ni = 13.38 mm2/s
T1 = 288 K
R = 287 J/kgK
K = 1.5
kr = 0.1 mm

Q: Calculate internal diameter of 2 m long pipe that can provide air flow rate of 500 m3/h, with 1500 mbar absolute pressure on the pipe start with 487 mbar pressure drop to pipe exit to open atmosphere. Pipe internal roghness is 0.1 mm and local resistance coefficient is K = 1.5. Air temperature is 288 K.

A: Calculation setup:
Input values:
q1 = 500 m3/h
p1 = 1500 mbar
p1 - p2 = 487 mbar
L = 2 m
ni = 13.38 mm2/s
T1 = 288 K
R = 287 J/kgK
K = 1.5
kr = 0.1 mm

Q: Calculate flow rate of air flowing through 2 m long pipe to open atmoshere with 5 mm inside diameter. Pipe internal roghness is 0.1 mm and local resistance coefficient is K = 1.5. Air temperature is 288 K. On the pipe start, air is under 1500 mbar absolute pressure.

A: Calculation setup:
Input values:
D = 5 mm
p1 = 1500 mbar
p2 = 1013 mbar
L = 2 m
ni = 13.38 mm2/s
T1 = 288 K
R = 287 J/kgK
K = 1.5
kr = 0.1 mm

Gas discharge calculation is based on the modified Darcy formula:

Read more about used theory on compressible gas flow theory page.

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

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