Edge

An edge "always connects two vertices by a straight line" (Blender 3.1 Manual: Mesh Structure). Edges are "the 'wires' you see when you look at a mesh in wireframe view" (Blender 3.1 Manual: Mesh Structure), and every face is bounded by them.

#Why edges matter in games

Edges are cheap in themselves; GPUs draw triangles, not lines. What makes edges important is the information attached to them.

• Loops and flow. Chains of edges form edge loops and edge rings. A loop continues through vertices with four edges and stops at poles (Blender 3.1 Manual: Mesh Structure). Good edge flow lets you select, bevel and deform a model cleanly.
• Hard and soft shading. You mark edges as sharp (hard) or smooth. On a hard edge the faces either side get separate normals, which means split vertices. Unity's Smoothing Angle setting decides "whether vertices are split for hard edges" (Unity Manual 2018.2: Model tab). See smoothing, hard edges and smoothing groups.
• UV seams. Seams are also marked on edges, and they split vertices the same way. See UV seams and islands.
• Silhouette. On a low-poly model, the edges on the outline are what you see against the sky. Edges spent on the silhouette usually matter more than edges inside flat areas. See silhouette.

#Faces per edge

On a closed, solid object, each edge borders exactly two faces. Meshy's glossary defines a manifold mesh as one where "every edge is shared by exactly two faces" (Meshy: Manifold). An edge with only one face is a border or hole. An edge with three or more faces is non-manifold. Blender's 3D Print Toolbox flags both kinds (Blender 3.6 Manual: 3D Print Toolbox).

#Vertex cost of hard edges

On the Unreal forums a user tested a cube: with all edges hard it imported with 24 vertices; smoothing the faces around one corner welded that corner and gave 22 (Unreal Engine Forums: Vertex Count & Light Map Vertex Count). Every hard edge you mark has a cost in vertices, even though the triangle count stays the same.

#Common mistakes

• Hard edges that are not on UV seams. They split vertices for no extra benefit and can cause seams in baking. Put hard edges on UV borders.
• Zero-length edges. Two vertices on top of each other leave an edge with no length. Maya's Cleanup can remove "edges with a zero length" below a tolerance you set (Maya 2017 Help: Cleanup Options).
• Wire edges. Edges with no face attached are loose geometry and do not render. See manifold and non-manifold geometry.
• Wasting edges on flat areas. Extra edges on a flat surface do not change shading or silhouette, unless you need them for vertex painting or deformation.

#In different tools

• Blender. Edges are a selection mode in Edit Mode. The Statistics overlay documents vertex, face and triangle counts (Blender 3.5 Manual: Viewport Overlays). Sharp edges are marked per edge; by default Blender treats an edge as sharp if it is "either non-manifold, or having at least one of its faces defined as flat" (Blender 3.1 Manual: Mesh Structure).
• Maya. The Poly Count HUD lists edges alongside vertices, faces, triangles and UVs (Maya 2026 Help: Heads Up Display (HUD) Options).
• Unreal Engine. The Static Mesh Editor reports triangles, vertices and UV channels, not edges (Unreal Engine Documentation: Static Mesh Editor UI). Once a mesh is in the engine, edges only exist as the sides of triangles.

#Related terms

vertex · face · edge loop · edge ring · support loop · smoothing, hard edges and smoothing groups · manifold and non-manifold geometry

#Further reading and watching