This is a way of getting feats or powers calculated via for Attack Potency, Destructive Capacity and for TNT Equivalence. Here are a few links that would help get started for that sort of thing.
For other miscellaneous means of Calculations such as what you would find on OBD or VSBattle Wiki, here are a means of what you would need to find to make those calcs.
Use the visuals of the Game, Comic, Manga, Movie/TV Show to help with the calcs. Or the description of the feat (Unless it is considered Hyperbolic or if the Lore is separate from the media or are different versions from one another).
Some with certain measurements such as Height, Width and Depth, multiply them together to get the Volume, which ever unit you get, convert them to cm^3, then multiple it by how ever powerful the means of destruction is to get joules, then convert it to which ever TNT unit to find the stat. here is the links for that: