In wireless sensor networks (WSN), capacity estimation and signal to noise ratio calculation are challenging problems with many research attentions. In this paper, which is a small part of a larger research, we propose two new methods to attain precise and approximation estimation of SINR distribution in WSN. These methods are combinations of probabilistic techniques and clustering approach, incorporating interference as noise in DS-CDMA method without using interference cancelation techniques. Clustering partitions the network to the two layers, sensors and Headers. This SINR distribution may lead us to estimate and calculate the WSN's throughput or capacity, which is an important parameter for performance measuring in such networks. Also we have investigated the effect of path-loss as one channel parameter on the SINR distribution, for both network layers.