With the increasing demand for wireless commu- nication systems, while Heterogeneous Networks (Het-Nets) are under study toward 5G technology in mobile communication systems, WiFi Access Points (APs) are considered a potential layer within those multiple Radio Access Technologies (RATs). Significant network capacity gain can be achieved not only through aggressive reuse of spectrum across the multiple tiers in the network, but also by integrating WiFi in the mobile network through additional spectrum in un-licensed bands. Different criteria should be investigated in order to allow both the WiFi APs and the end user to operate on the best suitable channel, where the basic one of those criteria is the "load" of the operating channels. We propose in this paper an accurate algorithm for the estimation of WiFi 802.11n physical channels load through 3 channels observations only. Once the channel load is estimated using the proposed algorithm, the channel assignment based on the minimal load value is acquired, thus providing faster response of an AP channel selection and faster end user connection for better Quality of Experience (QoE). Index Terms-WiFi Channel selection, 802.11n physical layer, Power Spectral Density, Heterogeneous Networks