The Root Mean Square (rms) speed is the square root of the average of the squares of the speeds of the molecules. From the relation $\frac{1}{2}m{v}_{rms}^2=\frac{3}{2}{k}_{B}T$, we can solve for $v_{rms}$: $v_{rms}=\sqrt{\frac{3k_{B}T}{m}}$ Alternatively, in terms of the molar mass $M$ and gas constant $R$: $v_{rms}=\sqrt{\frac{3RT}{M}}$ This is a standard measure of the average speed of particles in a gas at a certain temperature.