Flow rate Q

Flow rate Q is defined to be the volume of fluid passing by some location through an area during a period of time, as seen in Figure.  

In symbols, this can be written as 

Q = V / t,  

where 

V is the volume and

t is the elapsed time. 

The SI unit for flow rate is m³/s, but a number of other units for Q are in common use. 

 For example, the heart of a resting adult pumps blood at a rate of 5.00 liters per minute (L/min).  

Note that a liter (L) is 1/1000 of a cubic meter or 1000 cubic centimeters ( 10⁻³m³ or 10³cm³ ).

The precise relationship between flow rate Q and velocity v is

Q = A v,

where
A is the cross-sectional area and
v is the average velocity.