Discharge Coefficient

Definition - What does Discharge Coefficient mean?

Discharge Coefficient is the ratio of actual discharge through a nozzle or orifice to the theoretical discharge. Commonly known as coefficient of discharge, it is related to the flow and pressure loss through nozzles and the orifices in the fluid systems or fluid mechanics. It is denoted by “Cd” and is a dimensionless number.

In fluid mechanics, coefficient of discharge is the ratio of mass flow rate at the nozzle’s discharge end to that of the ideal nozzle working in ideal flow conditions.

Petropedia explains Discharge Coefficient

Mathematically, coefficient of discharge is expressed as:


Cd = coefficient of discharge

A = cross sectional area of orifice or nozzle from where fluid is flowing

M = mass flow rate (dm/dt)

p = density of fluid (dm/dV) where V is the volume

delta P = drop in the pressure across the two ends of the orifice

With the help of coefficient of discharge, one can estimate the resistance to the flow of fluid in a confined space (in a pipeline, or in an orifice) through the following equation:

K = 1 / square of coefficient of discharge

Where k is resistance to the flow.

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