Reynolds number is defined as the ratio of dynamic pressure to shearing stress.It is a non dimensional parameter.Reynolds number predicts the extent of turbulence in a fluid, based on how fast the fluid is flowing, the geometry of flow(depth and wide etc…) density and viscosity of fluid.
Mathematically,
Reynolds number (Re) = Dynamic Pressure (ρ v2) / Shearing Stress (μ v / L)
Re = ρ v2 / (μ v / L)
Re = ρ v L / μ
where
Re = Reynolds Number (non-dimensional)
ρ = density
v = velocity
μ = dynamic viscosity
L= characteristic length
Dimensional Formula of Density (ρ) =M1L-3T0
Dimensional Formula of Velocity(v) = M0L1T-1
Dimensional Formula of Dynamic viscosity(μ) = M1L-1T-1
Dimensional Formula of Length(L) = M0L1T0
Putting these values in above equation we get,
Dimensional Formula of Reynolds Number = (M1L-3T0)(M0L1T-1)(M0L1T0)/(M1L-1T-1)
Dimensional Formula of Reynolds Number = M0L0T0
Reynolds Number has no units (non dimensional).