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.