diff --git a/opm/core/grid/GridHelpers.cpp b/opm/core/grid/GridHelpers.cpp
index 85006cc3..03528a18 100644
--- a/opm/core/grid/GridHelpers.cpp
+++ b/opm/core/grid/GridHelpers.cpp
@@ -57,6 +57,17 @@ const double* beginCellCentroids(const UnstructuredGrid& grid)
     return grid.cell_centroids;
 }
 
+double cellCenterDepth(const UnstructuredGrid& grid, int cell_index) 
+{
+    double zz = 0.0;
+    for (int i=grid.cell_facepos[cell_index+1]-2; i<grid.cell_facepos[cell_index+1]; ++i) {
+        for (int j=grid.face_nodepos[grid.cell_faces[i]]; j<grid.face_nodepos[grid.cell_faces[i]+1]; ++j) {
+            zz += (grid.node_coordinates+dimensions(grid)*(grid.face_nodes[j]))[2];
+        }
+    }
+    return zz/8.0;
+}
+
 double cellCentroidCoordinate(const UnstructuredGrid& grid, int cell_index,
                                  int coordinate)
 {
diff --git a/opm/core/grid/GridHelpers.hpp b/opm/core/grid/GridHelpers.hpp
index cd9ad084..fc7bfcee 100644
--- a/opm/core/grid/GridHelpers.hpp
+++ b/opm/core/grid/GridHelpers.hpp
@@ -137,6 +137,13 @@ struct CellCentroidTraits<UnstructuredGrid>
 CellCentroidTraits<UnstructuredGrid>::IteratorType
 beginCellCentroids(const UnstructuredGrid& grid);
 
+
+/// \brief Get vertical position of cell center ("zcorn" average.)
+/// \brief grid The grid.
+/// \brief cell_index The index of the specific cell.
+double cellCenterDepth(const UnstructuredGrid& grid, int cell_index);
+
+
 /// \brief Get a coordinate of a specific cell centroid.
 /// \brief grid The grid.
 /// \brief cell_index The index of the specific cell.