Venturi Meter Flow Calculator

How to use the Venturi meter flow calculator

Enter the inlet diameter, throat diameter, discharge coefficient, differential pressure and liquid density. You get the flow rate and the throat velocity. Press × on Differential pressure to find the DP for a given flow.

Venturi meter flow formula

Q = C_d × (πd²/4) × √[2ΔP ÷ (ρ(1 − β⁴))]

Example

D = 100 mm, d = 60 mm, ΔP = 200 mbar, water:

• β = 0.6, Q = 68.0 m³/h

Flow vs DP (100/60 mm, water)

DP	Flow
10 mbar	15.2 m³/h
25 mbar	24.1 m³/h
50 mbar	34.0 m³/h
100 mbar	48.1 m³/h
200 mbar	68.0 m³/h
400 mbar	96.2 m³/h
600 mbar	117.8 m³/h

Venturi vs other DP meters

Element	Typical Cd	Permanent pressure loss	Straight run needed
Classical Venturi	0.98–0.995	5–20% of DP	Short
Flow nozzle	0.93–0.99	30–60%	Medium
Orifice plate	0.60–0.62	50–90%	Long

Where Venturis are used

• Large water and wastewater mains, where pumping energy matters.
• Slurries and dirty liquids, as the smooth shape does not trap solids.
• Irrigation and cooling-water systems.

For a 4–20 mA DP transmitter on a Venturi, use the square-root flow calculator to scale the signal.

Frequently asked questions

What is a typical Venturi discharge coefficient?

About 0.98–0.995 for classical Venturi tubes, much higher than the 0.6 of an orifice plate, because flow follows the smooth contraction.

Why use a Venturi instead of an orifice plate?

Venturis recover most of the pressure drop (permanent loss typically 5–20% of the DP), saving pumping energy, and handle dirty or slurry flows better.

What beta ratio is typical?

Between about 0.4 and 0.75 under ISO 5167-4.

How does a Venturi measure flow?

Fluid speeds up in the throat, lowering its pressure (Bernoulli). The pressure difference between inlet and throat is proportional to flow squared.

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