This paper investigates the windage power loss generated by helical gears rotating in pure air. A three-dimensional approach using computational fluid dynamics (CFD) code which has been validated for spur gear is adapted here in order to consider helix angle. The numerical approach is at first validated with the power losses measured in similar conditions. The influence of both width and helix angle values on the expelled volumetric flow rate and the windage losses are studied. Considering these observations, a correlation which is based on a classical approach used in turbomachinery is proposed.