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"These spells not only increase the interior dimensions of objects, while leaving the outer ones unchanged, they also render the contents lighter."
— Description[src]

The Extension Charm (Capacious Extremis) was a charm that expanded the internal dimensions of an object without affecting the external dimensions, enhancing its capacity, and rendering its contents lighter. This charm was advanced magic and heavily controlled by the Ministry.[1]


"Undetectable Extension Charm. Tricky, but I think I've done it okay; anyway, I managed to fit everything we need in here."
Hermione Granger explaining her use of the charm[src]

Extension Charms were advanced magic and subject to strict Ministry of Magic control. This was because of its potential to create breaches of the International Statute of Wizarding Secrecy. There was a law in place that Extension Charms were not to be cast for private use, but only for the production of objects. These objects had been individually approved for manufacture by the relevant Ministry Department.[1] Hogwarts school trunks (like the majority of wizarding luggage) were issued with these charms.[1] Family tents were also infused with this charm, in order to make them more inhabitable. The official cars used by the Ministry were also fitted with these charms as standard issue. 

FB-extension charm

Jacob Kowalski entering Newt's extended suitcase

Newt Scamander used the Extension Charm on a suitcase during the 1920s. He used the enlarged space to house the many magical creatures he collected during his trip around the world while gathering information for his upcoming book Fantastic Beasts and Where to Find Them.

Arthur Weasley used the Extension Charm, among others, on his Flying Ford Anglia. It was able to fit all of the Weasleys living at The Burrow at that time, Harry Potter, and all of their luggage comfortably. Molly did not recognise it for what it was, stating "Muggles do know more than we give them credit for, don't they?" Mundungus Fletcher cast this spell on an automobile he stole on Christmas of 1995 to transport the Weasleys and company to St Mungo's Hospital for Magical Maladies and Injuries. It managed to fit all of the above minus Arthur and Percy, as well as William Weasley, Hermione Granger, Alastor Moody, Remus Lupin, and Mundungus himself.[2]

Undetectable Extension Charm

Hermione Granger placed an Extension Charm on her beaded handbag

In 1997, Hermione Granger used this charm on her small beaded handbag so that she was able to pack all the supplies she believed she would need while hunting down Lord Voldemort's Horcruxes with Harry Potter and Ron Weasley. This included books, changes of clothes, money, Harry's Cloak of Invisibility, and healing supplies.[3] Eventually, Hermione also placed the portrait of Phineas Nigellus Black that had previously been in 12 Grimmauld Place in her bag as well[4] to prevent Severus Snape from spying on them.



The effects of the Extension Charm Hermione placed on her handbag

This sophisticated charm was used to expand an object's internal dimensions while retaining its external appearance. The charm also magically disguised itself so that no one but the caster (and those the caster confided about the charm in) can realise that this spell has been cast over the object, even if they were experiencing it. The charm also rendered the contents lighter.

Because Harry Potter had lived as a Muggle for years, he immediately recognised that in order to accommodate eight people and six trunks, the Weasley's Ford Anglia must have been enchanted to fit far more than its physical dimensions allowed. Likely aware of this, Arthur Weasley then showed Harry how the charm had affected the car.

Theoretically, a hundred wizards could take up residence in a toilet cubicle if they were sufficiently adept at these spells.[1]

Known practitioners[]

Known charmed items[]

Object Caster Notes
Newton Scamander's suitcase Newton Scamander Used by Newt Scamander to contain several magical beasts and document them, along with occasionally relocating these creatures to their natural habitats.
Basement of 9 Sherringford Square Newt Scamander Used by Newt Scamander to contain several magical beasts and document them, similar to his suitcase.
Flying Ford Anglia Arthur Weasley Used by Arthur Weasley to expand the inside of the automobile, allowing his entire family to fit inside at once.
Ministry cars Ministry of Magic Used by the Ministry of Magic as a security measure for transporting important people; regulated by the Ministry of Magic.
Hogwarts school trunks Hogwarts School of Witchcraft and Wizardry Used by Hogwarts students to contain all their school supplies; regulated by the Ministry of Magic.
Charmed Tents Ministry of Magic Used by wizards for camping out in the wilderness while providing comfort and necessities found in the common wizarding household; regulated by the Ministry of Magic.
Stolen Muggle car Mundungus Fletcher Used by the Order of the Phoenix to travel to St Mungo's without arousing suspicion.
Hermione Granger's beaded handbag Hermione Granger Used by the trio to contain various supplies while they searched for Lord Voldemort's horcruxes in order to destroy them.
Luna Scamander's suitcase Luna Scamander Used by Luna to contain magical creatures.
Victor Gridley's caravan Victor Gridley Used by Gridley to create space to live in.


Capacious is an English word meaning "having a lot of space",[5] derived from the Latin word capax, which means capacity. Extremis comes from a conjugation of the Latin extrēmus, meaning "extreme".

Behind the scenes[]


Extension Charm as seen in Harry Potter: Puzzles & Spells

  • The effects of this spell are similar to the "bigger on the inside" effects of the TARDIS in Doctor Who.
  • The effects of the spell are also very similar to Mary Poppins's carpet bag.
  • This charm appears to have a number of interesting side-effects when cast over an object. For example, when Hermione drops the bag she has cast this charm over in Harry Potter and the Deathly Hallows it makes a suspiciously loud thump (making it seem heavy), yet she carries the bag with ease (despite the number of objects inside).
  • In the American versions of Harry Potter and the Order of the Phoenix, the spell used on cars to increase their capacity is identified as the Enlarging Spell, though the spell goes unidentified in the original British text. Pottermore, however, clarifies that the spell used on the Weasley's Ford Anglia was the Extension Charm, thus making this embellishment non-canon.


Notes and references[]

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Writing by J. K. Rowling: "Extension Charms" at Wizarding World
  2. Harry Potter and the Order of the Phoenix, Chapter 23 (Christmas on the Closed Ward)
  3. Harry Potter and the Deathly Hallows, Chapter 9 (A Place to Hide)
  4. Harry Potter and the Deathly Hallows, Chapter 12 (Magic is Might)
  5. Merriam Webster Dictionary - capacious