There are different techniques which also depend on the organizational structure as a whole.
For instance, a team may have a “senior” expert in their field, a team leader, a supervisor, a department leader, a branch manager…
I’ve also worked with organizations that allocate a single expert to a project. Think of consultancies or social media agencies.
Then I’ve worked with factories or engineering companies, where a project is comprised of experts across a large set of skills, with niche professionals jumping between multiple teams.
Jeff Bezos has shared his “Two-Pizza rule”, stating that a team is too large if they can feed themselves at the room with two large pizzas. Depending on how you look at this, I’d venture 7 to 10 people should suffice.
In project management, 6 to 8 subordinates is optimal for less experienced managers. Professional ones, especially having worked with this particular team for at least a year, can handle 10 to 12 subordinates effectively.
Your mileage may vary, but this should be a good starting point.