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Orifice Flow Calculator — Flow Rate from Diameter, Pressure Drop & Cd
Calculate incompressible liquid flow through an orifice from diameter, pressure drop, fluid density and discharge coefficient.
Last updated: September 17, 2026
Results
Enter positive diameter, density and Cd plus non-negative pressure drop
Formula, example and assumptions
Q=Cd·A·√(2ΔP/ρ), A=πd²/4.
A 10 mm orifice with a 100 kPa pressure drop through water produces a flow on the order of litres per second depending on Cd.
- This simplified equation is for incompressible flow and does not model gas choking.
- Cd must represent the actual orifice geometry and Reynolds-number regime.
FAQs
What is the discharge coefficient?
Cd accounts for contraction and losses that make real flow lower than the ideal Bernoulli prediction.
Can I use this for compressed gas?
Not reliably. Compressible gas flow can choke and needs a compressible-flow model.