How is punishment for a red card decided?

If a Player is sent off, it is a matter of fact the player will be suspended 7 days after the date of the game, as set out by The FA in the Discipline Handbook.

The length of ban and disciplinary penalty points depends on the type of misconduct. Please check page 12 of the Grassroots disciplinary guide for information on this. See link below. 

https://en.calameo.com/read/0012302350a12fb961b0a?authid=jqdy6WLsm4nO&_gl=1*kutz49*_ga*OTg0NzU1NzM3LjE2NTU5OTM4Njk.*_ga_T81QCG9DQL*MTY1NjU4MDg3Ni4xNi4xLjE2NTY1ODA4ODguNDg.