How many faces are there in an icosahedron?

An icosahedron has 20 faces. In the familiar regular icosahedron, those faces are 20 congruent equilateral triangles arranged into a highly symmetrical three-dimensional solid.

The icosahedron is one of the five Platonic solids, whose faces are identical regular polygons and whose vertices have the same arrangement. Its other basic counts are 30 edges and 12 vertices. At every vertex, five triangular faces meet.

The name comes from Ancient Greek roots associated with the number twenty. Its dual Platonic solid is the dodecahedron: the centers of an icosahedron’s faces correspond to the vertices of a dodecahedron, and vice versa.

The word can also describe less symmetrical polyhedra with 20 faces, including forms whose faces are rhombi rather than triangles. In ordinary trivia and geometry questions, however, “icosahedron” almost always means the regular convex icosahedron. It is also widely recognized as the shape of a 20-sided die, often called a d20.