A: Area
C: Discharge coefficient
d: density ( water density = 1000kg/m³ )
D: Diameter
g: Gravity 9.8 m/s²
K: Flow coefficient (Kv)(Cv)
Q: Flow rate
SG: Specific gravity (1 for water)
v: Flow 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 km 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 km m mi mm nmi yd		cm ft in km 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		at atm bar inH2O inHg kp/cm² kPa lbf/ft² lbf/in² mbar mca mce mH2O mmca mmce mmH2O mmHg mmWC mmWs MPa mWC mWs N/mm² Pa PSI torr		g/cm³ g/l g/m³ g/ml g/mm³ kg/cm³ kg/l kg/m³ lb/ft³ lb/in³ lb/gal (UK) lb/gal (US) mg/cm³ mg/l mg/m³ oz (Av)/gal (UK) oz (Av)/gal (US) oz (Av)/ft³ oz (Av)/in³ t/m³		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		at atm bar inH2O inHg kp/cm² kPa lbf/ft² lbf/in² mbar mca mce mH2O mmca mmce mmH2O mmHg mmWC mmWs MPa mWC mWs N/mm² Pa PSI torr		g/cm³ g/l g/m³ g/ml g/mm³ kg/cm³ kg/l kg/m³ lb/ft³ lb/in³ lb/gal (UK) lb/gal (US) mg/cm³ mg/l mg/m³ oz (Av)/gal (UK) oz (Av)/gal (US) oz (Av)/ft³ oz (Av)/in³ t/m³		cm ft in km 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	at atm bar inH2O inHg kp/cm² kPa lbf/ft² lbf/in² mbar mca mce mH2O mmca mmce mmH2O mmHg mmWC mmWs MPa mWC mWs N/mm² Pa PSI torr		g/cm³ g/l g/m³ g/ml g/mm³ kg/cm³ kg/l kg/m³ lb/ft³ lb/in³ lb/gal (UK) lb/gal (US) mg/cm³ mg/l mg/m³ oz (Av)/gal (UK) oz (Av)/gal (US) oz (Av)/ft³ oz (Av)/in³ t/m³		cm ft in km 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.