To Calculate Area of a voronoi polygon (and length and width), you need to find out the vertices of voronoi edges. To find the vertices you have to create Delaunay triangulation from the set of points. The vertices of the Voronoi edges are located at the circumcenters of the Delaunay triangles. The Circumcenter function returns a matrix of set of circumcenters. Look into Voronoi Diiagrams for more info.
TR = delaunayTriangulation(P);
C = circumcenter(TR);
To find area of a voronoi polygon you can use convhull function.
[~,area]=convhull(vertices);
