https://worldofwarcraft.com/en-us/news/2113741/guild-advancement-and-you#:~:text=Guild%20Experience%20and%20Perks&text=Guild%20members%20can%20contribute%20experience,at%20least%2080%25%20guild%20members.
https://wow.gamepedia.com/Guild_advancement
https://wowwiki.fandom.com/ru/wiki/%D0%9F%D1%80%D0%BE%D0%B4%D0%B2%D0%B8%D0%B6%D0%B5%D0%BD%D0%B8%D0%B5_%D0%B3%D0%B8%D0%BB%D1%8C%D0%B4%D0%B8%D0%B8
"With the new Guild Advancement system, members can help contribute guild experience to level up their guild in a similar manner to how you'd level up a character. Through a number of personal or group actions that each guild member undertakes, the guild earns experience. The experience in turn goes toward raising the guild's level. Guild members can contribute experience to their guild level by completing quests, daily quests, killing dungeon and raid bosses with a group comprised of at least 80% guild members, and winning rated Battleground matches with a group comprised of at least 80% guild members.
An exception to the 80% rule is for five-person dungeons, which only require 3/5 people to be in the guild to earn guild experience and achievements.* The amount of experience gained scales, with 3/5 guild members granting 50% normal guild xp, 4/5 giving 100%, and 5/5 giving 125% guild xp. The amount gained from each boss scales with your level relative to the boss's level, with Heroic bosses worth even more (1.5x). It pays off to have a full group of guild members!
Another exception is when visiting the older 40-person raids, which only require 25% guild participation (10 members) to earn experience and achievements."
January 22, 2011