# Discharge Coefficient

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Discharge coefficient, abbreviated as $$C_d$$, also called coefficient of discharge, a dimensionless number, is the ratio of actual discharge to the theoretical discharge.

## Discharge Coefficient formulas

 $$\large{ C_d = \frac { \dot m_f } { \rho \; Q } }$$ $$\large{ C_d = \frac { \dot m_f } { A_c \; \sqrt { 2 \; \frac{ \Delta p}{ \rho} } } }$$ $$\large{ C_d = \frac { \dot m_f } { d^2 \; \frac {\pi}{4} \sqrt { 2 \; \frac{ \Delta p}{ \rho} } } }$$ $$\large{ C_d = \frac { \dot m_f } { A_c \; \sqrt { 2 \; \rho \; \Delta p } } }$$ $$\large{ C_d = \frac { \dot m_f } { d^2 \; \frac {\pi}{4} \sqrt { 2 \; \rho \; \Delta p } } }$$

### Where:

 Units English SI $$\large{ C_d }$$ = discharge coefficient $$\large{ dimensionless }$$ $$\large{ A_c }$$ = area cross-section of flow constriction $$\large{ ft^2 }$$ $$\large{ m^2 }$$ $$\large{ \rho }$$  (Greek symbol rho) = density of fluid $$\large{\frac{lbm}{ft^3}}$$ $$\large{\frac{kg}{m^3}}$$ $$\large{ \dot m_f }$$ = mass flow rate $$\large{\frac{lbm}{sec}}$$ $$\large{\frac{kg}{s}}$$ $$\large{ \pi }$$ = Pi $$\large{ dimensionless \; constant }$$ $$\large{ d }$$ = pipe inside diameter $$\large{ in }$$ $$\large{ mm }$$ $$\large{ \Delta p }$$ = pressure drop across constriction $$\large{\frac{lbf}{in^2}}$$ $$\large{Pa}$$ $$\large{ Q }$$ = volumetric flow rate $$\large{\frac{ft^3}{sec}}$$ $$\large{\frac{m^3}{s}}$$

## Related Discharge Coefficient formula

 $$\large{ C_d = \frac { Q_o } { A_o \; \sqrt { 2 \; G \; h } } }$$ (orifice area) (orifice gravitational constant)

### Where:

$$\large{ C_d }$$ = discharge coefficient

$$\large{ A_o }$$ = orifice area

$$\large{ h }$$ = orifice center of head

$$\large{ Q_o }$$ = orifice flow rate

$$\large{ G }$$ = orifice gravitational constant