What is Dunbar's Number?

You might notice a shift in the air when your company hits a specific size. It happens around the time you walk into the break room and realize you do not know the name of the new hire making coffee. You might feel a sudden disconnect from the front lines of the work.

This phenomenon is often linked to a concept called Dunbar’s Number.

Proposed by British anthropologist Robin Dunbar in the 1990s, this theory suggests there is a cognitive limit to the number of people with whom one person can maintain stable social relationships. Based on the size of the human neocortex, that number is approximately 150.

It is important to understand that this limit is not about how many faces you can recognize or how many names you can memorize. It is about relationship quality.

Dunbar defined these relationships as knowing who each person is and how each person relates to every other person in the group. It is the ability to maintain a coherent mental map of the complex web of interpersonal connections.

In a small startup of five people, the communication lines are simple. Everyone knows what everyone else is doing. As you scale, the number of connection points grows exponentially.

Once you exceed 150 people, the cognitive load required to maintain those relationships exceeds the brain’s hardware capabilities. You can no longer rely on implicit trust and shared context to get things done.

For founders, hitting this number often feels like a crisis. This is the stage where employees start complaining that the company has become corporate or bureaucratic.

When a group exceeds 150, the mechanisms that regulate behavior change. In groups under 150, peer pressure and personal reputation are usually enough to keep the organization aligned. If someone is slacking, the group knows and corrects it socially.

Above 150, peer pressure loses its efficacy because the social bonds are too weak. This is why you suddenly need formal structures:

• Defined HR policies
• Written mission statements
• Middle management layers
• Structured communication channels

If you try to run a 200 person company like a 20 person family, chaos usually follows.

History and industry show us how organizations adapt to this limit. Military units, like companies in the army, are typically capped around this number to ensure the commander can personally know every soldier.

In business, W.L. Gore and Associates (makers of Gore-Tex) famously capped their factories at 150 employees. Once a parking lot was full, they would simply build another factory rather than expanding the existing one. They found that keeping units small preserved culture and speed.

We must ask ourselves if technology changes this math. Dunbar’s research was based on physical proximity and biological limits. Do tools like Slack, Zoom, and Notion allow us to expand our cognitive capacity?

It is possible these tools simply create the illusion of connection without the depth required for a stable social relationship. We do not yet have definitive data on how digital-first environments impact this cognitive ceiling.

As you build, monitor your organization as it approaches this threshold. You may not be able to change the biology of the human brain, but you can design your company structure to work with it rather than against it.