How many Dragon Balls are needed to summon the wish-granting dragon Shenron?

How to get close to this number

Collection quests settle on a small set of numbers, and seven is the most common of them across folklore, religion and fiction. A quest needs enough objects to sustain a search and few enough to be memorable and countable at a glance; seven satisfies both, which is why it recurs everywhere from fairy tales to modern franchises.

This one is rare on this site in that the answer is genuinely fixed. Fictional counts usually drift as a franchise expands and adaptations add material, but here the number is embedded in the title of the work itself, so it cannot move. If anything, the franchise doubled down on it rather than diluting it.

The detail in the explanation is the good one: a second set of seven exists, under different rules and summoning a different dragon. So the number is stable while what it refers to is not, which means a question about how many are needed has to specify which set — and the answer being the same for both is a design choice rather than a coincidence.