The performance of an IEEE 802.11 station heavily depends on the selection of an AP (Access Point) that the station is associated with to access the Internet. The conventional approach to the AP selection is based on the received signal strength called RSSI (Received Signal Strength Indication) from APs within the transmission range. This approach however, might yield unbalanced traffic load among APs as the station chooses an AP only based on the signal strength, instead of considering the AP load and the level of contention on medium access. Accordingly, the station that is associated with the highest-RSSI AP might suffer from poor network performance. In this paper, we propose a new association metric, EVA (Estimated aVailable bAndwidth) with which a station can find the AP that provides the maximum achievable throughput among scanned APs. EVA is designed to estimate the available bandwidth on a channel with respect to a station that is to join a WLAN (Wireless Local Area Network). A station equipped with EVA observes a channel state in a per-slot basis, and yet does not request any external information from nearby APs or neighbor stations. Our estimation mechanism is non-intrusive, fully distributed, and independent of the infrastructure. Through simulation study, we evaluate the accuracy of the estimation and show that EVA-based association yields enhanced throughput performance compared with the legacy scheme.