The church plan is that of a Latin cross with five aisles. The central nave vaults reach forty-five metres while the side nave vaults reach thirty metres. The transept has three aisles. The columns are on a 7.5 metre grid. However, the columns of the apse, resting on del Villar's foundation, do not adhere to the grid, requiring a section of columns of the ambulatory to transition to the grid thus creating a horseshoe pattern to the layout of those columns. The crossing rests on the four central columns of porphyry supporting a great hyperboloid surrounded by two rings of twelve hyperboloids (currently under construction). The central vault reaches sixty metres. The apse is capped by a hyperboloid vault reaching seventy-five metres. Gaudí intended that a visitor standing at the main entrance be able to see the vaults of the nave, crossing, and apse, thus the graduated increase in vault loftiness.
here are gaps in the floor of the apse, providing a view down into the crypt below.
The columns of the interior are a unique Gaudí design. Besides branching to support their load, their ever-changing surfaces are the result of the intersection of various geometric forms. The simplest example is that of a square base evolving into an octagon as the column rises, then a sixteen-sided form, and eventually to a circle. This effect is the result of a three-dimensional intersection of helicoidal columns (for example a square cross-section column twisting clockwise and a similar one twisting counter-clockwise).
Essentially none of the interior surfaces are flat; the ornamentation is comprehensive and rich, consisting in large part of abstract shapes which combine smooth curves and jagged points. Even detail-level work such as the iron railings for balconies and stairways are full of curvaceous elaboration.