# Water Flow Rate Through an Orifice

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

## Water Flow Rate Through an Orifice formula

 $$\large{ Q_w = 0.0865 \; C_d \left( \frac{d_o}{4.654 } \right)^2 \; \sqrt { \frac{ p_1 \;-\; p_2 }{ SG } } }$$

### Where:

 Units English Metric $$\large{ Q_w }$$ = water flow rate $$\large{\frac{ft^3}{sec}}$$ $$\large{\frac{m^3}{s}}$$ $$\large{ d_o }$$ = diameter of orifice $$\large{ in }$$ $$\large{ mm }$$ $$\large{ C_d }$$ = orifice discharge coefficient $$\large{dimensionless}$$ $$\large{ p_1 }$$ = primary pressure $$\large{\frac{lbf}{in^2}}$$ $$\large{Pa}$$ $$\large{ p_2 }$$ = secondary pressure $$\large{\frac{lbf}{in^2}}$$ $$\large{Pa}$$ $$\large{ SG }$$ = specific gravity of water $$\large{dimensionless}$$