List of largest nebulae

Below is a list of the largest known nebulae so far discovered, ordered by actual diameter. This list is prone to change because of inconsistencies between studies, the great distances of nebulae from our stellar neighborhood, and the constant refinement of technology and engineering.

Caveats

Nebulae have no standardized boundaries, so the measurements are subject to revision. Furthermore, scientists are still defining the features and parameters of nebulae. Because of these rapid developments and adjustments, this list may be unreliable.
Lyman alpha nebulae around quasars can have sizes between 15 kpc and 460 kpc. Especially large Enormous Lyα nebula can have large sizes of ≳100 kpc. Farina et al. 2019 table 5 has an extensive compilation of Lyman alpha nebulae around quasars. For now this list contains only the largest ELANs, with sizes larger than 300 kpc.