Histogram is the commonest method for the size estimation of query result in many commercial database systems. Several histogram methods presented in the past have certain limitations in practicability due to their lack of guarantee of the accuracy of the estimation. In this paper, the author presents two kinds of new histogram methods, which are easy to use and can guarantee the accuracy of the estimation. Otherwise, the effect of different data distributions to histograms is discussed in the paper, and some important parameters of data distribution are introduced to help produce better histograms.