When I first took an Agile class many years ago, I was taught that the optimal team size was 7, plus or minus 2 — so anywhere between 5 and 9 members. Fast forward a few years, and the Scrum Guide adjusted this to: “the optimal team size is between 3 to 9 people.” The Scaled Agile Framework, on the other hand, defines Agile teams as cross-functional groups of 5 to 11 individuals. In 2022, the Scrum@Scale Guide got even more specific, suggesting an “optimal team size of 4.6 people,” referencing research it said was from Harvard. I’ve come across several advocates recently insisting the magic number is 6.
I will review the research and give you my proposal for the optimal size for teams of knowledge workers.
The first study that set the “magic number” at 7 was published back in 1956, but it wasn’t actually about team size at all — it focused on experiments in attention and memory. The 1970 study by Hackman and Vidmar, which produced the now-famous 4.6 number, aimed to find the relationship between team size and performance. They concluded, “Results showed that size had negligible effects on performance.” A follow-up questionnaire was administered to the undergraduate participants, asking which group size was too big and which was too small for their 15-minute assignments. Their answers averaged out to 4.6. The takeaway? A team size of 4-5 people might be best for maintaining satisfaction during small tasks that have no impact on customers and with no regard for output performance.
Most other studies focused on teams where all members worked on the same task without any leadership or structure — a scenario far removed from the realities of modern business environments. I found only one study that examined real-world situations: Jennifer S. Mueller from the Wharton School in 2012 concluded that individual performance in teams starts to decline once the team exceeds 5 members. She attributes this decline to what she calls Relation Loss, where individuals in larger teams perceive less support from their peers.
Yes, many industry leaders and writers refer to theories like Amdahl’s Law, cite coordination and communication costs, or share anecdotes to conclude that smaller is better, often suggesting 5, 6, or 7 members as ideal. Jeff Bezos even has his famous “two-pizza team” rule.
But now, let me share my own analysis, experience, and conclusions.
All of the studies, except for Mueller’s, were conducted in laboratory environments using participants who previously did not work together. Their tasks were simple, very short, and without any intrinsic value for customers. I assume that every business has the opposite kind of work: employees with long-standing relationships, solving complex issues over a period of time to create meaningful outcomes for customers. Even if all we cared about was team member satisfaction, the real-world equation is dramatically different from an artificial lab simulation. These studies involved teams working on the same task at the same time. But real teams are not static like that. Even in a small five-person team, each day will have instances of members working individually, helping others one-on-one, huddling 2 or 3 at a time, and occasionally collaborating as a full group. Given the experimental structure, we must conclude that the results are not directly applicable at all.
Mueller’s research focused on the intrateam costs of interaction. She identified three types of performance loss: motivation, coordination, and relational/support. Is anyone surprised that costs increase as the number of people increases? I’d be much more interested in a study about the benefits of teamwork or strategies for improving outcomes. If you’re concerned about these potential areas of performance loss, I’d recommend focusing on how to address team members’ issues regarding motivation, coordination, and support.
The best business team I managed spanned two continents with 6 team members and 1 close adjacent peer. The best tech team I led had 25 tightly knit engineers: hardware, software, and firmware specialists. There were two stellar teams I worked with as an Agile coach, one with 20 part-time marketers in one location, the other with 16 dedicated creative professionals spread across four time zones.
These four teams were very different in almost every superficial characteristic. However, they shared three key elements: Each team had a clear understanding of who their customers were and how their individual and collective contributions served those customers. They were built on a leadership model—not just from the top down, but with each member leading on his or her area of stewardship. Lastly, they operated with a culture of active, pervasive accountability. When those three things are present, you don’t need to worry much about motivation, coordination, or support loss.
So, what’s the optimal team size? The answer is: it depends. The ideal size will vary based on the people involved and the type of work to be done. People aren’t fungible assets; they are individuals. And the work to be done is not identical from team to team. As a leader, you’ve got to evaluate the variables, listen to your people, make a decision, and course-correct based on results as an active participant rather than a distant manager.
Ultimately, the best thing you can do to improve team effectiveness isn’t obsessing over team size — it’s implementing a solid customer-centric, product-based strategy, providing great leadership, and fostering accountability.
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