Dunbar's number
Dunbar's number, proposed by anthropologist Robin Dunbar in the 1990s, is a cognitive limit on the number of stable social relationships a human can maintain — approximately 150 for casual acquaintances, with tighter inner circles at 50, 15, and 5. Applied to engineering organisations, Dunbar's number explains why engineering cultures change qualitatively as headcount crosses ~150 — the informal coordination that worked at 50 stops working.
The applied implication: at 5-15 engineers, everyone knows everyone's project and decisions can be made in the kitchen. At 50, a single weekly all-hands keeps coherence. At 150, you need explicit org structure, documented decisions, and process — the informal coordination that worked at 50 collapses, often messily. Companies that scale from 50 to 200 engineers in a year report this as the most disruptive transition: technical talent that thrived in the small-team mode struggles in the formal-process mode, and process structures that worked at 50 (e.g., a single shared standup) become absurd at 200. Forewarned teams plan for the transition deliberately; many discover it retrospectively.
Related terms
- Team Topologies
Team Topologies, codified in the 2019 book by Matthew Skelton and Manuel Pais, is a framework for organising engineering teams using four team types and three interaction modes.
- Conway's Law
Conway's Law, formulated by Melvin Conway in a 1968 paper, states that any system's design mirrors the communication structure of the organisation that built it.