Analysis of handwritten characters (allographs) plays an important role in forensic document examination. However, so far there lacks a comprehensive and quantitative study on individuality of handwritten characters. Based on a large number of handwritten characters extracted from handwriting samples of 1000 individuals in US, the individuality of handwritten characters has been quantitatively measured through identification and verification models. Our study shows that in general alphabetic characters bear more individuality than numerals and use of a certain number of characters will significantly outperform the global features of handwriting samples in handwriting identification and verification. Moreover, the quantitative measurement of discriminative powers of characters offers a general guidance for selecting most-informative characters in examining forensic documents.