Stiking Power

Taking this from the Vs Battles Wiki

Striking strength describes the power behind the character’s physical blows. Generally, anything that has to do with the character’s actions instead of passively holding up weighs is about this category. While lifting strength is a static value which can be measured in units of weight or mass, striking strength is different. It relies more on “action” which is a combination of speed and mass and could be the best measured in joules. As such striking strength requires a whole different classification system
 * Class H: Human class. Punches and kicks usually range in the few hundred joules but there are a few heavy weight boxers who’re pushing slightly above a thousand joules per hit.
 * Class KJ: Kilojoule class. Slightly superhuman to outright wall busting attacks.
 * Class MJ: Megajoule class. Attacks can have effects similar to a hand grenade. At high end we’re talking about outright building busting attacks.
 * Class GJ: Gigajoule class: Attacks carry the force of many tons of TNT explosives. Building level to low end multi city block level.
 * Class TJ: Terajoule class. Attacks carry the power of kilotons of explosives. Punches literally comparable to a nuke.
 * Class PJ: Petajoule class. Attacks carry megatons of energy. Citybusting punches.
 * Class EJ: Exajoule class. Attacks carry gigatons of energy. Characters whose blows can outright destroy an island.
 * Class ZJ: Zetajoule class. Attacks carry teratons of energy. Country-wrecking punches.
 * Class YJ: Yottajoule class. Attacks carry petatons of energy. Continent-busting physical strikes.
 * Class NJ: Ninajoule class. Attacks carry exatons of energy. Planetoid and moon-buster physical attacks.
 * Class XJ: Tenajoule class. Attacks carry zetatons of energy. Characters in this category can usually physically bust planets.
 * Class XKJ: Tenakilojoule class. Attacks carry yottatons of energy. A character like this can destroy a large planet like Jupiter with a punch.
 * Class XMJ: Tenamegajoule class. Attacks carry thousands to millions of yottatons of energy. Characters like this have nearly enough power to destroy a star.
 * Class XGJ: Tenagigajoule class. Attacks carry millions to billions of yottatons of energy. Star-busting punches to various degrees.
 * Class XTJ: Tenaterajoule class. Attacks ranging from 10 mili-Foe to 10 Foe of energy. Physical blows approaching or even somewhat surpassing the power of a Supernova.
 * Class XPJ: Tenapetajoule class. Attacks ranging between 10 Foe and 10,000 Foe. Characters at this level can bust the Solar System with no effort.
 * Galactic Class: Characters have enough energy to physically destroy our Milky Way Galaxy. Otherwise could be called Class BXKJ (bitenakilojoules), as it requires at least 10^61 joules to destroy our galaxy with a single boom (contended).
 * Universe Class: For crazy characters who can destroy everything in our Universe with a single punch.
 * Immeasurable: For things even crazier than that. Believe me, they exist.

The “J” part is referring to joules and used to distinguish the striking strength classes from the old strength system.