# Euler's formula for polyhedra

Euler's formula for polyhedra is the earliest known equation in topology.
If *F* is the number of faces of a polyhedron, *E* the number of edges, and *V* the number
of vertices,
Euler's formula can be written as

*F* - *E* + *V* = 2.

For example, the surface of a cube has six
(square) faces, twelve edges, and eight vertices and, sure enough, 6 - 12
+ 8 = 2. The quantity *F* - *E* + *V* is known as the Euler characteristic.