Conical coordinates, sometimes called sphero-conal or sphero-conical coordinates, are a three-dimensional orthogonal coordinate system consisting of concentric spheres (described by their radius r) and by two families of perpendicular elliptic cones, aligned along the z- and x-axes, respectively. The intersection between one of the cones and the sphere forms a spherical conic.

The conical coordinates ${\displaystyle (r,\mu ,\nu )}$ are defined by

with the following limitations on the coordinates

Surfaces of constant r are spheres of that radius centered on the origin

whereas surfaces of constant ${\displaystyle \mu }$ and ${\displaystyle \nu }$ are mutually perpendicular cones

and

In this coordinate system, both Laplace's equation and the Helmholtz equation are separable.

The scale factor for the radius r is one (h_r = 1), as in spherical coordinates. The scale factors for the two conical coordinates are