In the episode Flatline the power is being drained from the Tardis which resulted in the shrinking to a handy bag sized version. As a last resort to avoid being crushed by a train the Doctor activated Siege Mode which made the little blue box look all rufty toughty and impregnable.

However, if the Tardis had been functioning at full power and Siege Mode was activated would it still be small or would it be a different size? It strikes me that a battle mode which prevented the occupants from escaping is a bad idea!

  • 5
    The word "siege mode" by definition means that it prevents outsiders from entering, so I think keeping people from getting out might just be a side effect. In other words, even if it was a cube of 2 meters on the side, people still wouldn't be able to get out.
    – Mr Lister
    Oct 24, 2014 at 10:43
  • By the way, if a TARDIS has full power, it has much better ways of escaping than just letting people exit through the door!
    – Mr Lister
    Oct 24, 2014 at 10:48
  • 3
    The TARDIS wasn't shrinking because it was being drained of power, it was shrinking because it was being drained of dimensions. If it weren't for the fact that the TARDIS is the TARDIS, it probably would've gone 2D within the first act of the episode.
    – Brian S
    Oct 24, 2014 at 14:20

2 Answers 2


We don't have enough information regarding "siege mode" to know conclusively what apparent size the TARDIS portal would end up being.

What we do know:

  • The TARDIS' dimensional energies as well as the physical dimensions of the external aspects of the TARDIS were being affected. The TARDIS grew smaller in relation to its appearance in our universe due to its dimensions being absorbed by the two-dimensional aliens.

If we are to assume, the TARDIS found itself without sufficient power to escape a circumstance that required the "siege mode" it would likely change its appearance proportionally.

  • If the TARDIS were to enter "siege mode" under non-dimensionally challenged conditions, it is safe to assume the cubic mode would be comparable and proportional to its shrunken dimensions.

When we first see the portable TARDIS, before Clara put it in her purse, it was about 12 inches long.

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It does shrink further during the episode.

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The cube we see later is about three inches. Assuming it didn't shrink further, the proportions would be about 2 to 1. A six inch TARDIS becoming 3 inch cube.

  • I suspect this would make the TARDIS a cube approximately 4 feet depending on the absolute size of the Police Box appearance.

It isn't the size of the TARDIS under "siege mode" that matters, it's the impregnability. This is one of those instances where "size doesn't matter."


My guess is that it would be the in proportion of the sizes of the minitardis and the minisiege. A rough estimate might be 7ft x 7ft.

  • Do you have any basis for thinking this or references?
    – user20310
    Oct 25, 2014 at 21:35

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