You can use pressure drop in pipe calculator for pressure drop and flow rate calculation for all Newtonian fluids (gases and liquids) with constant density (incompressible flow) in closed, round or rectangular duct.

If the system that you are analyzing has more than one pipe, you can use pipe network analysis calculator

Pressure drop calculator is suitable for laminar and turbulent flow regime. You can't use this calculator for compressible gas flow where the pressure of the gas is changing more than 5-10%. For that purpose, you can use one of available gas pressure drop calculators.

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PreDropWaterQ, D, L, kr, Δp

Task:
Calculate pressure drop in round pipe with flow of 5 m^{3}/h,
pipe length 100 m, internal pipe diameter of 25 mm and pipe roughness of 0.1 mm.
Flowing fluid is water with density of 1000 kg/m^{3}.
Local resistance can be negligible K = 0.

Solution: Pressure drop is: 4.78 bar

PreDropWaterΔp, D, L, krQ

Task: Calculate flow rate of water through closed round pipe with internal diameter of 25 mm, pipe length of 100 m. Pipe line connecting reservoir on the elevation of 20 m above the pipe exit with water flowing to open atmosphere. Reservoir is under atmospheric pressure. Pipe roughness is 0.1 mm.

Solution: Flow rate is: 3.16 m3/h

PreDropAirQ, H, W, L, krΔp

Task:
Calculate pressure drop of 2000 m^{3}/h of air flowing through closed
rectangle channel to open atmosphere. Chanel width is 400 mm and height is 250 mm.
Chanel is with surface roughness of 0.01 mm. Local resistance coefficient is line is 3.5.
Chanel length is 85 m.

Solution: Pressure drop is: 298.96 Pa