A method of determining the d.c. magnetization characteristic of a laminated core using overlapping joints, when the mean flux density is less than half the saturation value, has been given by Phear and Mallock. This method is now extended to include any value of the mean flux density and to increase the accuracy of calculation over the range covered by Phear and Mallock, their work being followed to the fullest possible extent in the present paper.The results are expressed in terms of the increase per joint of the total m.m.f. of the core with varying mean flux density, since in this form they can be applied directly to determine the d.c. magnetization characteristic of any laminated core.Calculated and test results applicable to Mumetal only are given in the present paper, but bearing in mind the change in the ferric saturation value, the conclusions become generally applicable to other magnetic materials such as the silicon-iron steels.Among other important conclusions arrived at is the result that it is possible for a plain butt joint to require a smaller increase in m.m.f. than an overlap joint over quite an appreciable range of the mean flux density.