Multiverse

Throughout the series, multiple "dimensions" have been shown to exist in the Phineas and Ferb universe. These "dimensions" vary slightly or significantly from the canonical dimension where the main characters live.

Nature of The Multiverse
Although they are frequently referred to as "other dimensions", the "dimensions" of Phineas and Ferb in no way resemble real life theoretical dimensions. In real life, what defines a higher or lower dimension is the amount of directions in which one may travel in them. Phineas and Ferb obviously live in the 3rd dimension, being able to travel sideways, backwards and forwards, and up and down. Other dimensions in the series always have the same amount of directions, and are therefore also in the third dimension. They are, instead, separate universes to themselves, but as Baljeet showed in Phineas and Ferb: Across the Second Dimension, they are connected by a stream of energy. Phineas and Ferb therefore live in a "multiverse".

Physics of The Multiverse
Until the TV movie Phineas and Ferb: Across The Second Dimension premiered, not much was known about the actual workings of the Phineas and Ferb multiverse. In the film, 2nd dimension Baljeet gives a lecture on how one travels through the multiverse. It appears as though the "dimensions" are connected. There is a clockwise energy flow which connects each of the "dimensions". To travel into an alternate dimension, it appears that one must create a portal which accesses this flow of energy. Since the energy flows in a clockwise direction, accessing Phineas's dimension would require traveling against the natural flow of energy. Baljeet explains that while this is possible, it would require an enormous amount of energy to travel in such a way. Initially, they do indeed open such a portal. However, it is unstable, and closes soon after Phineas announces he will not enter his dimension until he finds the now captured Perry.

Later on, Phineas is able to access his own dimension by traveling clockwise through the entire "grid" of "dimensions" in the multiverse until he gets back to his own.

Main Dimensions
this part of the list is for the main six dimensions The first dimension is the normal dimension, and the dimension of Phineas and Ferb,The first dimension first appeared in "Rollercoaster". The second dimension was dimension ruled by Doofenshmirtz-2, and the dimension of Phineas-2 and Ferb-2 The second dimension first appeared in "Phineas and Ferb The Movie:Across The 2nd Dimension". The third dimension is a dimension that has a Baby alien who is bigger than Phineas and Ferb, The third dimension first appeared in "It's a Mud, Mud, Mud, Mud World". The fourth dimension is a dimension that has Giant Floating Baby Heads which is smaller or bigger than Phineas and Ferb, The fourth dimension first appeared in "Phineas and Ferb The Movie:Across The 2nd Dimension". The fifth dimension is a dimension that is possibly two as since in "Isabella and the Temple of Sap" it was red and had serpent-like aliens while in the website of "Phineas and Ferb The Movie:Across The 2nd Dimension" it was blue and more space-like than the other, Phineas and Ferb did'nt go to this dimension wich is odd as since Baljeet-2 said you have to go clockwise altoughthey could have just cutted it from the movie, The fifth dimension first appeared in "Phineas and Ferb The Movie:Across The 2nd Dimension". The sixth dimension is a dimension that has human hillbillies wich are drawn in crude than Phineas and Ferb, The sixth dimension first appeared in "Phineas and Ferb The Movie:Across The 2nd Dimension".
 * The 1st Dimension
 * The 2nd Dimension
 * The 3rd Dimension
 * The 4th Dimension
 * The 5th Dimension
 * The 6th Dimension