Dimensional transcendentalism Dimensional transcendentalism was the state wherein an object ' s interior was bigger than its exterior , an effect made possible by transdimensional engineering . The Fourth Doctor once explained the principle to Leela by using the analogy of how a larger cube might appear to be able to fit inside a smaller one were the larger cube further away , yet immediately accessible at the same time . He described this as " a key Time Lord discovery " . ( TV : " The Robots of Death " ) Rory Williams later surprised the Eleventh Doctor with his understanding of the principle , that the inside was " another dimension " . ( TV : " The Vampires of Venice " ) The relationship between the interior and exterior sizes of a TARDIS could be controlled via the dimensional control . ( TV : " Checkmate " ) Dimensionally transcendental objects other than TARDISes included Dalek time machine s , ( TV : " The Chase " ) the SIDRAT s constructed by the War Chief , ( TV : " The War Games " ) the Genesis Ark , ( TV : " Doomsday " ) the Doctor ' s pockets , ( TV : " The Runaway Bride " , " The Vampires of Venice " ) , the Towers of Canonicity and Likelihood on Gallifrey , ( PROSE : " The Gallifrey Chronicles " ) and clown car s from the planet Semtis . ( PROSE : " Shroud of Sorrow " ) After Jack Harkness , Gwen Cooper and Rex Matheson entered a PhiCorp warehouse , Jack stated that it was bigger on the inside . ( TV : " Dead of Night " ) Sometimes when a TARDIS was dying , its dimension dam s would start to break down in what was called a " size leak " . The Eleventh Doctor described it as " All the bigger on the inside starts leaking to the outside . It grows . " This happened to the Doctor ' s TARDIS , as it was dying on Trenzalore . Here it served as the Doctor ' s tomb in an alternative timeline in which the Time Lords never granted the Doctor a new cycle of regenerations at the conclusion of the Siege of Trenzalore . Prior to his battle , the Eleventh Doctor and Clara Oswald discovered the ruined TARDIS relative to his future when they went to Trenzalore . It still appeared as a police box but was much larger . Clara described it as " one hell of a monument . " ( TV : " The Name of the Doctor " ) The Dalek s were capable of creating dimensionally transcendent factory ships . ( PROSE : " War of the Daleks " ) The Seventh Doctor temporarily expanded the interior dimensions of a boarding house in Cheldon Bonniface to allow all the guests at Bernice Summerfield ' s wedding to stay there . ( PROSE : " Happy Endings " ) Upon meeting the " Teselecta " , " a robot worked by tiny people " , the Eleventh Doctor , wondering how they could all fit inside , briefly suggested that it was bigger on the inside until he discovered it was via basic miniaturisation sustained by a compression field . ( TV : " Let ' s Kill Hitler " ) It ' s bigger on the inside . Many of the Doctor ' s companions were in awe of police box that was larger within , often commenting that " it ' s bigger on the inside . " ( TV : " The Three Doctors , Robot , Rose , The Runaway Bride , Smith and Jones , The Eleventh Hour , The Bells of Saint John , The Pilot " ) The Doctor looked forward to this , ( TV : " The Vampires of Venice " ) and was excited at an opportunity to exclaim it himself . ( TV : " The Husbands of River Song " ) Rose Tyler expected Adam Mitchell to say the phrase , and said it for him ; the Ninth Doctor mused she could learn some things from Adam when he instead gave the proper name for it . ( AUDIO : " The Other Side " ) Kevin , due to being a robotic t - rex , found the inside rather claustrophobic . ( COMIC : " Space Squid " ) When Bill Potts , who had initially believed the TARDIS to be a secret room and then a lift , finally shouted the phrase , the Doctor and Nardole expressed glee at finally hearing her say it . ( TV : " The Pilot " ) However , one version of Clara surprised the Doctor by saying the reversed phrase , " It ' s smaller on the outside . " ( TV : " The Snowmen " ) Journey Blue later said this phrase . ( TV : " Into the Dalek " )