The package provides an easy and flexible user interface to
customize page layout, implementing auto-centering and
auto-balancing mechanisms so that the users have only to give
the least description for the page layout. For example, if you
want to set each margin 2cm without header space, what you need
is just \usepackage[margin=2cm,nohead]{geometry}. The package
knows about all the standard paper sizes, so that the user need
not know what the nominal 'real' dimensions of the paper are,
just its standard name (such as a4, letter, etc.). An important
feature is the package's ability to communicate the paper size
it's set up to the output (whether via DVI \specials or via
direct interaction with pdf(La)TeX).

Homepage:
https://ctan.org/pkg/geometry
