Abstract: In the paper, the confusions about the different stress intensity factor formulas in the foreign references for the double cleavage drilled compression (DCDC) specimens are clarified theoretically and numerically. It is proved that the formulas for DCDC obtained by Plaisted et al. using a modified solution for a pair of short cracks at the opposite edges of a circular hole in an infinite plate subjected to compression, and using an Euler-Bernoulli beam solution for a long crack, respectively, are both inadequate, with errors existing either in the formulation or in the model-based principle. A new formula of stress intensity factor for DCDC is obtained by fitting the wide-ranging numerical results of finite element analysis; the maximum error of the new formula is less than 7%. The new formula is also simpler in form than that given by Jenne et al., and with larger applicable range as compared to the formulas of He et al. for both the dimensionless crack length and the dimensionless plate width. Furthermore, for the newly proposed single cleavage drilled compression (SCDC) specimens, a stress intensity factor formula for SCDC is also formulated, and the maximum error of the formula for SCDC is less than 5%. The two formulas derived in this paper can be used for testing mode-I fracture toughness of brittle materials using either the DCDC or the SCDC specimens.