The IEEE 802.11 standard has been extensively deployed all over the world. Many studies have been put on its performance, especially throughput. Most research focused on the analysis of saturated throughput, but non-saturated situation is more usual in practice. By extending a saturation throughput model, a concise and novel model is proposed in this paper, which can be used to analyze both saturated and non-saturated conditions. Moreover, the model can also deal with the heterogeneous condition, which allows stations to have different traffic. Different access mechanisms and packet payloads are used in simulation to validate it, and the results show that the model is accurate.