A: Area
C: Flow coefficient (non-dimensional)
d: density ( water density = 1000kg/m³)
D: Diameter
g: Gravity 9.8 m/s²
K: Flow coefficient (dimensional) (Kv)(Cv)
Q: Flow rate
SG: Specific gravity (1 for water)
v: Velocity
Δh: Head Drop (high of fluid)
ΔP: Pressure Drop

C	=	Q	/ [ SQRT ( 2 · g ·	Δh	) ·	A
		cfs cfh cfm cm³/s gpm (US) in³/s l/h l/min l/s m³/h m³/min m³/s yd³/h yd³/min yd³/s		cm ft in m mi mm nmi yd		a ac cm² ft² ha in² km² m² mm² yd²

C	=	Q	/ [ SQRT ( 2 · g ·	Δh	) · (	D	)² · π / 4 ]
		cfs cfh cfm cm³/s gpm (US) in³/s l/h l/min l/s m³/h m³/min m³/s yd³/h yd³/min yd³/s		cm ft in m mi mm nmi yd		cm ft in m mi mm nmi yd

C	=	Q	/ [ SQRT ( 2·	ΔP	/	d	) ·	A	]
		cfs cfh cfm cm³/s gpm (US) in³/s l/h l/min l/s m³/h m³/min m³/s yd³/h yd³/min yd³/s		atm bar inH2O inHg kp/cm² kPa in/ft² lbf/ft² MPa mbar mH2O mmH2O mmHg mmWC mWC N/mm² Pa PSI torr		g/cm³ g/mm³ kg/m³ lb/ft³		a ac cm² ft² ha in² km² m² mm² yd²

C	=	Q	/ [ sqrt(2·	ΔP	/	d	) · (	D	)²·π/4]
		cfs cfh cfm cm³/s gpm (US) in³/s l/h l/min l/s m³/h m³/min m³/s yd³/h yd³/min yd³/s		atm bar inH2O inHg kp/cm² kPa in/ft² lbf/ft² MPa mbar mH2O mmH2O mmHg mmWC mWC N/mm² Pa PSI torr		g/cm³ g/mm³ kg/m³ lb/ft³		cm ft in m mi mm nmi yd

C	=	K		· sqrt(	d	/2) / [(	D	)² · π/4]
		cfs cfh cfm cm³/s gpm (US) in³/s l/h l/min l/s m³/h m³/min m³/s yd³/h yd³/min yd³/s	atm bar inH2O inHg kp/cm² kPa in/ft² lbf/ft² MPa mbar mH2O mmH2O mmHg mmWC mWC N/mm² Pa PSI torr		g/cm³ g/mm³ kg/m³ lb/ft³		cm ft in m mi mm nmi yd

K = Cv, when K is referenced in [gpm] [psi] units.
K = Kv, when K is referenced in [m³/h] [bar] units.