Properly speaking TARDISes are
best
described as "spaces," rather than "objects."
Most
TARDISes are Dimensionally Transcendental, meaning that
they are bigger on the inside than the outside. This
effect is achieved by making a TARDIS's interior a
quasi-dimensional continuum located outside of
Time.
This Micro-Universe
is created using Transcendental
Block-Transfer
Equations that don't interface with
Normal Space in a traditional way. Crewmembers will find
that for every month they spend inside a TARDIS they will
age slightly less then a week.

Dimensional Transcendentalism is
achieved using
the Relative
Dimensional Stabilizer, which time maps the
para-dimensional interior though null-space
and the Vortex
and onto the
Exo-Shell's exterior outlet. This Time Mapping forms the
Dimensional Gateway. The dimensionally transcendental
nature of a TARDIS can be thought of as a hypercube (i.e.
a 4 dimensional square).

A TARDIS's interior is composed
of
a complex web of
bio-mathematics and exitonics with
a finite
multi-dimensional
mass,
which
usually
totals about 68 thousand metric tons.
While a TARDIS's minimum interior
volume is about the size of an atom, its maximum volume
is about one trillion cubic kilometers.

The interior of a TARDIS is
incapable of holding an object that is several miles
across without extensive block-transfer modifications. In
such a state one could walk for 10,000 years with only a
few hours of rest a day and never reach the end. The
great size of a TARDIS interior is also rumored to be
linked to the vast depths and capabilities of a Time
Lord's mind.