The sealevel equation allows to compute the sealevel variations induced by surface ice loads, taking into account for the deformations of the solid Earth and for the changing shape of the geoid. It is a tool of particular interest for people working in the fields of glacio-isostatic adjustment and global geodynamics. Here we present the sealevel equation and we solve of it using a "finite elements" method. The companion software SELEN will be published here in the future.