A method is presented to derive the approximate weight functions, by using a new condition on the crack mouth, for edge cracks in the semi-infinite or finite plate under Mode I loadings. This method requires only one information, say, the reference stress intensity factor (SIF), K-r. Numerical examples show that the present method is efficient in evaluation of the SIFs for edge cracks subjected to the polynomial loadings on the crack faces. Copyright (C) 1996 Elsevier Science Ltd.