A simple way to calculate the level of effort required is to look at past project performance and compare it with the current project plan to identify the current project team velocity.
You can then use the formula: current velocity/project estimate = resources required.
It’s important to calculate resources needed for a project so that you take the right amount of the team’s time. Resource too little, and they won’t have enough time to complete the work, and if you resource too much, you might inadvertently be pushing them to waste time or work slowly to fill in the time.