The Lubuntu manual shows screenshots where the install is taking place on a system with 25GB of storage.
For whatever reason, Lubuntu doesn’t come with minimum system requirements (which is understandable given the notion that it is not a one-size fits all kind of thing but at the very least, a baseline for the storage space taken post-install [without internet] is something that would be common or predictable enough to post requirements for but I digress).
Here you go:
