We present a method to determine the throughput of an extended service set in an IEEE 802.11 network. The method combines two tools. The first tool takes the location of access points and a floor plan and uses an RF propagation model to predict the spatial distribution of SNR and interference that mobile stations will experience. The second tool takes the SNR of mobile stations and predicts system throughput, based on an analytical Markov chain model. The method can help to intelligently plan WLAN deployment.