Default Shortcut: N
Menu Path: Modify > Mirroring > Calculate Symmetry
The Calculate Symmetry command will attempt to find symmetrical components on an object by looking for vertices which should be mirrors of each other topologically, based on a central seam. If a single edge is selected when this function is called, the mirror seam will be determined by that edge. If there is no selection or anything other than a single edge is selected, the mirror seam will be determined automatically based on the axis selected in the options. Symmetry will also be enabled for the object (see Symmetry Mode Toggle).
Once symmetry has been calculated and as long as it is enabled, edits made to one side of the model will be reflected in the other side. Unlike with instance mirroring (see Instance Mirror Toggle), you can edit either side (or both sides at once) of the mesh. The shape will also subdivide properly and displacement painting will be mirrored as well. Newly created geometry added via commands such as Bevel and Extrude should also be mirrored properly automatically.
Note that this command will not immediately move any geometry to make it visually symmetrical, (for that, use Restore Symmetry after calculating symmetry, or use Mirror Geometry) but future geometry edits will move affected geometry to make it symmetrical. This means that you can leave portions of your model asymmetrical even while you are working with symmetry. Just don't edit those parts while symmetry is enabled.
- Choose the axis along which the symmetry will be performed. Note that this command uses the object's local axis, which means the object does not need to be in the center of the scene for symmetry to be calculated properly. (You may wish to use Recenter Object Axis to ensure the object's axis is in the proper location relative to its geometry.)
- Vertices which are within this distance from the center of the mirror plane will be marked as though they are on the mirror seam. If some vertices are not being properly detected as along the mirror seam, you may need to increase this tolerance or adjust their position before calling Calculate Symmetry.