Flip Normals (inverted faces)

In newer versions of Blender the previously available Tool Shelf buttons Flip Direction and Recalculate, typically used to flip inverted surfaces that made meshes appear inside-out, have been moved to the main Mesh menu upper-left of the 3D View. As the option is now context sensitive it only appears as a menu option in Edit Mode.

Design note: the Mesh menu is specific to Edit Mode and does not appear unless that particular editing context is active.

Flip Selected Faces

To access the option and/or correct an inside-out or inverted face, first select the errant mesh element in Edit Mode [1] (using vertex, edge or face) and from the Mesh menu upper-left click Normals [2] then Flip [3] from the options that appear – Mesh » Normals » Flip. Alternatively use Alt + N to access the Normals context menu then select Flip. The highlighted inverted face/s will immediately invert based on their current orientation.

Design note: when selecting errant faces using vertices or edges make sure all component elements are included to the degree that the inverted faces highlight.

The option to flip or invert faces [1] is an Edit Mode option only (accessible only when editing meshes), click Mesh » Normals » Flip [2 & 3] with an individual face or group selected.

Recalculate Faces

As an alternative to selectively inverting faces, or re-orientating a large mixed selection so everything points in one direction,  inwards or outwards, use Recalculate Outside (Shift + N) or Recalculate Inside (Shift + Ctrl + N) options. To do this and force the orientation in one direction or the other, in Edit Mode select the entire mesh (A) and access the Mesh menu. Here select Normals » Recalculate Outside to flip faces/selections outwards, or Normals » Recalculate Inside to invert selections inwards – Mesh » Normals » Recalculate Outside/Inside.

Design note: in previous versions of Blender Recalculate tended to orientate faces randomly depending on the predominance of inwards or outwards facing surfaces prior to use. For Blender 2.8+ this is no longer the case, Recalculate Inwards and Recalculate Outwards forceably re-orientate selections based on the option selected, either in or out but not both.

For instances where surfaces are randomly facing one way or the other [4], or there are too many to select and manually process, use Recalculate Inwards/Outwards [5] to force everything to face the same direction, in or out, regardless – make a selection (individual, group or all) then click the Mesh menu, Normals then Recalculate Inwards/Outwards.

Face Orientation

To assist determining which way a face might be pointing, especially if Backface Culling is not disabled in Viewport Overlays or Viewport Shading options (depending on the viewport display mode) or a given materials Settings properties, Blender 2.8+ includes an option to colour tint faces based on their orientation, RED for surfaces pointing inwards and BLUE for those pointing outwards, making it much easier to see at a glance what’s going on, which then allows for individual faces to be flipped or recalculated as needed. To use, click the Overlays button upper-right of the 3D View [6] and from the menu select Face Orientation [7] – Overlays » Face Orientation. Everything will immediately tint blue/red based on their orientation. To disable, repeat, select Overlays » Face Orientation.

Design note: if X-Ray (Alt + Z) is active for any of the Viewport Shading modes, Wireframe, Solid etc., Face Orientation won’t work.

If Backface Culling is disabled (off) it can be difficult to determine which way a given surfaces is pointing because both front and back of the mesh are the same. In this situation using the Overlays [6] setting Face Orientation [7] can help as it tints surfaces based on their orientation, inwards or outwards.