--- /dev/null
+.. _aspect_ratio_3d_page:
+
+***************
+Aspect ratio 3D
+***************
+
+The **Aspect Ratio 3D** mesh quality criterion calculates the same parameter as the :ref:`aspect_ratio_page` criterion, but it is applied to 3D mesh elements: tetrahedrons, pentahedrons, hexahedrons, etc.
+
+* The **Aspect Ratio** of a **tetrahedron** 3D element defined by vertices {a,b,c,d } is calculated by the formula:
+
+ .. image:: ../images/formula1.png
+ :align: center
+
+* Other element types like polyhedron, pentahedron and hexahedron use the following formula:
+
+ .. image:: ../images/formula2.png
+ :align: center
+
+**To apply the Aspect Ratio 3D quality criterion to your mesh:**
+
+#. Display your mesh in the viewer.
+#. Choose **Controls > Volume Controls > Aspect Ratio 3D** or click **"Aspect Ratio 3D"** button of the toolbar.
+
+
+ .. image:: ../images/image144.png
+ :align: center
+
+ .. centered::
+ "Aspect Ratio 3D" button
+
+ Your mesh will be displayed in the viewer with its elements colored according to the applied mesh quality control criterion:
+
+ .. image:: ../images/image86.jpg
+ :align: center
+
+
+**See Also** a sample TUI Script of a :ref:`tui_aspect_ratio_3d` operation.
+
