The number of developers needed for an app depends on its complexity, the timeline, and your budget. A simple app can be handled by a single developer, while a complex app might require a team, with different members focusing on areas like frontend, backend, database management, software development, and security. For larger teams, you may also need a project manager or product manager to coordinate tasks and ensure everything runs smoothly. Remember, more developers can speed up the development process, but it also means higher costs. Consider your specific needs and constraints when deciding the size of your team.