# Reynolds number

The Reynolds number $\mathrm{Re}$ is a dimensionless quantity that gives a measure of the ratio of inertia forces $\left( \rho {\bold \mathrm V}^2 \right)$ to viscous forces $\left( {{\mu {\bold \mathrm V}} \over {L}} \right)$ and therefore quantifies the relative importance of these two types of forces for given flow conditions.