Which Dragon Ball episodes are filler?
Filler exists because television cannot wait for a monthly or weekly manga. Toei's Dragon Ball anime ran alongside Toriyama's serialization and repeatedly caught up with it, so the studio invented episodes, stretched fights, and added whole arcs. The famous five-minute Namek explosion occupying many episodes is pacing, not strictly filler, but the invented material is easy to catalog: the Wedding Dress and Mt. Five Element material in classic Dragon Ball, and in Z the Garlic Jr. saga, the Other World Tournament, and beloved single episodes like Goku and Piccolo learning to drive.
Kai, covered in the Library's own page on what changed in Kai, was built as the correction: a recut of Z following the manga closely, cutting Z's 291 episodes to 167 in its complete form and removing nearly all invented arcs. A viewer who wants the manga's story watches Kai; a viewer who wants the 1990s experience, score, pacing, and all, watches Z knowing a fifth of it is television invention.
GT and Super invert the question. GT (1996 to 1997, 64 episodes) has no manga source at all, so nothing in it is filler and nothing is canon in the manga sense; Toriyama's actual role on it is the subject of its own Library page. Super's anime and manga are parallel tellings from shared outlines, so episodes without manga equivalents, like the baseball episode, are better called anime-original than filler, and many fans rank them among the show's best.
For collectors of physical media, filler knowledge is purchasing knowledge: episode counts on box sets, the difference between Z and Kai sets, and the value of the Dragon Box (which preserves Z as broadcast) all turn on it. The Library's home video page compares the sets; this page is the map of what is inside them.
