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Venturi Flow Equation and Calculator

Fluids Flow Engineering
Hydraulic & Pneumatic Design Engineering
Fluid Flow Design and Engineering

Venturi Flow Equation and Calculator

A Venturi meter is used to measure the flow rate through a tube or volumetric flow rate, Q.

A venturi tube can also be used to mix a liquid with a gas and siphon into the venturi flow. If a pump forces the liquid through a tube connected to a system consisting of a venturi to increase the liquid speed (the diameter decreases), a short piece of tube with a small hole in it, and last a venturi that decreases speed (so the pipe gets wider again), the gas will be sucked in through the small hole because of changes in pressure. At the end of the system, a mixture of liquid and gas will appear.

Venturi Tube

Mass Flow


Density equation


Mass flow rate equation


Mass flow rate derivation

Qmass = ρ · Q


Q = volumetric flow rate (m3/s, in3/s)
Qmass = Mass flowrate (kg/s, lbs/s)
A1 = area = Π · r2 (mm2, in2)
A2 = area = Π · r2 (mm2, in2)
r1 = radius inlet at A1 (mm, in)
r2 = radius inlet at A2 (mm, in)
p1 = Measured pressure (Pa, lb/in2)
p2 = Measured pressure (Pa, lb/in2)
ρ = density (kg/m3, lb/in3)

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