Dunbars number
Dunbar’s Number and Team Design
Dunbar’s Number, proposed by British anthropologist Robin Dunbar, suggests that humans can maintain stable social relationships with approximately 150 people. This concept has significant implications for organizational and team design, particularly for a CTO managing engineering teams.
Key Implications for CTOs and Organizational Design
1. Limits on Team Size and Communication Overhead
- Dunbar’s research suggests different layers of relationship strength:
- 5 close relationships (e.g., co-founders, key leadership team)
- 15 strong relationships (e.g., direct reports, core product/engineering leads)
- 50 meaningful relationships (e.g., key managers and senior engineers)
- 150 stable relationships (e.g., wider org, broader team within a business unit)
- Beyond 150, relationships become more transactional, leading to increased bureaucracy, silos, and inefficiencies.
2. Engineering Team Structure and Scaling
- Early-stage startups: Communication is fluid, and most engineers interact directly with leadership.
- Growth-stage companies (~50-150 engineers): The transition from a single engineering team to multiple teams and units becomes necessary. CTOs must introduce clear reporting structures, processes, and communication cadences to avoid breakdowns.
- Beyond 150 engineers: Teams start operating in silos unless there are deliberate efforts to maintain connectivity, such as cross-team rituals, documentation, and internal tooling.
3. The Need for Subdivisions and Pods
- Spotify Model (Squads, Tribes, Guilds): Organizations like Spotify address Dunbar’s Number by breaking engineering teams into smaller, autonomous units (e.g., Squads of 6-12, Tribes of ~50).
- Two-Pizza Teams (Amazon): Amazon’s model limits teams to a size that can be fed with two pizzas (~8-10 people), reinforcing small, high-trust teams.
- Conway’s Law: Team structures influence system architecture. Keeping bounded teams with clear ownership helps avoid monolithic dependencies.
4. Leadership and CTO Span of Control
- A CTO should not directly manage more than 5-8 people (aligning with Dunbar’s inner circle).
- Engineering managers can handle 7-10 direct reports before team cohesion weakens.
- Beyond ~150 engineers, a VP of Engineering or other leadership layers become critical to maintain alignment, communication, and cultural cohesion.