The measurement of the displacement at the crack mouth of three-point bend specimens is compared to the measurement of load-line displacement for crack-length and J-integral evaluation. For crack-length determination by the unloading technique, the correction that must be made when using a clip gage mounted on knife edges is derived from load-line and crack-mouth opening displacements expressed as a function of crack length. Experimental results with tough steels show excellent agreement between the crack lengths determined by the two types of displacement measurements. The J integral can be evaluated using either method. The agreement between the two methods of J evaluation depends essentially on the evaluation of crack length. It is concluded that the J integral may be measured easily with a clip gage mounted at the crack mouth of three-point bend specimens.