How this calculator works
The coefficient is the measured flow divided by the ideal flow for the same opening and driving energy. Choose either pressure drop with density or hydraulic head with gravity. The reported resistance coefficient uses opening velocity Q/A as its reference, so K = 1/Cd squared. This is not automatically the permanent-loss coefficient of a pipe fitting or an orifice meter with pressure recovery. No upstream pipe-area correction is included.
Formula
Cd = Q/[A sqrt(2 delta p/rho)] = Q/[A sqrt(2gH)]. Mass flow = rho Q. For a circular opening d = sqrt(4A/pi). K = 1/Cd^2 under the stated velocity-head convention.
Worked example
An area of 0.01 m2 and head 2 m at g = 10 m/s2 give ideal flow 0.06324555320 m3/s. Measured flow 0.03794733192 m3/s gives Cd = 0.6 and K = 2.777777778.
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Frequently asked questions
Can a coefficient exceed one?
It can indicate that the chosen head, area or ideal model does not match the measurement. Review the setup before treating the value as a calibration.
How do I use mass flow?
Divide mass flow in kg/s by fluid density in kg/m3 to obtain Q in m3/s. Pressure-based results also report mass flow.
Is the diameter output a measured bore?
It is the circular diameter equivalent to the entered area. It does not establish the actual opening shape.