In general, highly detailed 3D meshes are often large and time-consuming to download. In order to address the problem, the amount of 3D data is reduced by decimating triangles that has little influence on visual quality. However, since few schemes for quantitative evaluation have been established yet, subjective evaluation is often used. While 1D and 2D digital signals exist only on sampling points, there is no "sampling points" in 3D meshes that makes it difficult to evaluate the differences of two meshes. In this paper, a computational scheme to measure the error between two meshes is proposed. The error is measured by dividing 3D meshes into some 2D planes and then further segmenting the 2D planes to pixels. Our algorithm handles not only the geometric error but also color differences.