Thermal comfort in ventilated spaces depends mainly on air temperature, air speed and turbulence intensity. Mean air speed is commonly measured with omnidirectional hot sphere sensors, whereas directionally sensitive measurement instruments and CFD-simulations normally give the mean velocity vector. The magnitude of the mean velocity vector in turbulent room air flows can be much lower than the mean air speed due to different time averaging processes. This paper studies the difference both experimentally and theoretically as a function of turbulence intensity. A correction method was developed for calculating estimates for omnidirectional mean air speed and turbulence intensity from directional air velocity data. The method can be applied to the calculation of draught risk and thermal comfort from CFD-simulation results.