Mass flow rate is the mass of a substance which passes through a given surface per unit of time.
m=ρ*V*A
where,m = mass flow rate, ρ= density, V = velocity ,A = flow area
For example, when Density of the liquid or gas(kg/m3) = 62.44, Velocity of the liquid or gas(m/s) = 1 m/s, Flow Area of the Liquid or gas(m2) = 2, then Mass Flow Rate = 124.88 kg/s.