The industrial applications of Electrochemical Machining (ECM) technology are limited due to difficulties in tool design, monitoring and control, and sludge generation and disposal. An accurate modeling and prediction of interelectrde gap (i.e. the gap between tool electrode and workpiece electrode) is one of the most important steps to minimize these difficulties. The interelectrode gap distribution depends on electric field distribution which is a function of many process parameters varying in space and time during electrochemical dissolution process. This paper proposes a model and numerical approach to determine the gap distribution. The model is based on determining the electric field in the interelectrode gap and finding a cathode (tool) boundary which will satisfy the Laplace Equation for potential distribution and all other boundary conditions to achieve the desired workpiece shape. The proposed method incorporates the variation of electrochemical machinability and, hence, is applicable to ECM with both non-passivating and passivating electrolytes. The proposed method does not require iterative redesign process, therefore, it provides excellent convergence and computing accuracy. The verification experiments have been conducted using a specially developed electrolytic cell and an industrial scale ECM system. A close agreement has between theoretical and experimental results.