There are a lot of resources scattered all over Internet about how salary or equity should be determined whenever you either found a start or join one. The thing is that there's no clear answer. It's more of the heuristic at start.
Buffer has released the way the calculate salary and equity including the spreadsheetwith all calculations.
(Role x Experience + Choice) x Loyalty = Salary
Role x Choice / Risk Layer + Seniority = Equity