In this paper, we study the VoIP capacity of IEEE 802.11b (DCF), i.e., the maximum number of simultaneous voice calls that can take place in a WLAN cell. This capacity is highly dependent on the chosen codec and on the distance from the access point (AP) to the users. Thus several codecs are studied, namely G711, GSM-EFR, and G723.1. All users are assumed to be at a fixed distance from the AP. The quality of voice calls is evaluated thanks to the E-model. Simulation results provide the following results: G711 allows up to 5 simultaneous calls, GSM-EFR up to 12, and G723.1 up to 18 for a voice quality greater than R=70 and a network delay of 20ms.