In orthogonal frequency division multiplexing (OFDM) systems, in order to overcome distortion caused by multipath fading, channel estimation is performed. Pilot symbol assisted channel estimation is effectual way to obtain channel state information. However, use of pilot symbols, leads overhead and the number of pilot symbols should be kept as minimum as possible. In this study, in order to evaluate the optimum pilot density, channel state information is obtained by using two dimensional (2-D) pilot based channel estimation. The analytical and simulated optimum pilot intervals in frequency and time direction are determined in terms of mean squared error (MSE). Then these intervals related to channel's coherence time (T-c) and bandwidth (B-c) at 0.9 correlation coefficient. It is seen from the results that by using approximately 2.4 pilot symbols per B-c,B-0.9, and per T-c,T-0.9 the optimum pilot interval can be calculated easily.