IEEE 802.11 k is an extension of the IEEE 802.11 specification for radio resource measurements. In an IEEE 802.11 k-enabled wireless LAN, an access point or other network element may request from a client or another access point to monitor and report the load of a channel. We call the latter a channel monitoring station. In this paper we propose a mechanism for a channel monitoring station to efficiently derive accurate values of channel load.We especially focus on optimizing the duration of channel monitoring and thus minimize the impact on applications. Note that such mechanisms are critical for the success of new sharing regimes such as cognitive radio and open spectrum access.