This paper describes a new numerical procedure for analysing earthing grids buried in horizontally stratified multilayer earth. The procedure is very efficient and general. The total number of layers and the total number of metallically disconnected earthing grids are completely arbitrary. A single earthing grid can be positioned in several layers. The procedure is based on an integral equation formulation. Earthing grid conductors are subdivided into segments and the average potential method is used. Efficiency and generality of the computation procedure are based on the successful application of numerical approximations of two kernel functions of the integral expression for the potential distribution within a single layer which is caused by a point current source. Each kernel function of the observed layer is approximated using a linear combination of 15 exponential functions. Extension from the point source to a segment of the earthing grid conductor is done by integrating the potential contribution due to a line of point current sources along the segment axis. This computational procedure gives highly accurate results in a short execution time.