We propose a novel contention window management algorithm that adjusts contention window size in dense wireless network environments. In the algorithm, a station estimates the number of neighboring stations by observing its number of freezes while attempting wireless channel accesses. Then, station adopts a new contention window size for further frame transmissions. We evaluate the proposed algorithm with the NS-3 simulator. The simulation results show that our algorithm outperforms existing works in terms of delay, throughput, collision rate, and frame delivery ratio.