The Scrum Team is small

The Scrum Team is small enough to stay nimble. At the same time, it is large enough to be able to generate something useful and valuable in each Sprint.

The official Scrum recommendation is that the Scrum Team should have ten or fewer members, but that the optimal size can be much smaller (SCHWABER; SUTHERLAND, 2020). These numbers include the Scrum Master and Product Owner, who may also exercise the accountability of a Developer.

In reality, when considering the number of members of a Scrum Team, we expect that:

its members will be able to communicate effectively to manage themselves. The number of communication channels grows exponentially with the number of people involved. As such, larger teams have greater communication and coordination difficulties, which makes self-management harder or even impossible.
its members collectively have all the knowledge and skills necessary to produce one or more done Increments of the product according to the Definition of Done, in each Sprint. This work translates into end-to-end, done features that represent value to the customers and users, rather than parts of the features, layers, or components.
its members are able to produce enough visible value in each Sprint so that they can generate release opportunities and obtain feedback from the customers and other stakeholders at the Sprint Review meeting on what has been produced.

When the product is very large, we can use more than one Scrum Team to work in a coordinated fashion on the same product, sharing the same Product Goal, Product Backlog and Product Owner. In this case, each of these teams has its size defined in accordance with the observations in this section.

Fun fact: changes in recommended size

The original article on Scrum, presented at a conference in 1995 (SCHWABER, 1997), stated that the team to develop a product should have between three and six members. The first published book on Scrum (SCHWABER; BEEDLE, 2002) defined the size of this team at seven plus or minus two members – that is, between five and nine members. The book referred to a famous article by the cognitive psychologist George A. Miller, who argued that the number of objects that an average human being is able to keep in his short-term memory is seven, plus or minus two (MILLER, 1956).

The original 2009 Scrum Guide, which defined the Scrum Team as a Scrum Master, Product Owner and Development Team, maintained this recommendation of seven plus or minus two members for the optimal size of the Development Team (SCHWABER, 2009).

In 2011, the creators of Scrum realized that even smaller teams can be successful. With this, the recommended number of members for the Development Team changed to no less than three and no more than nine (SCHWABER; SUTHERLAND, 2011).

In 2020, the Development Team ceased to exist, and the Scrum Team began to be composed of the Developers, the Scrum Master, and the Product Owner. As a result, the official recommendation now refers to the Scrum Team as a whole, and the numbers have changed, indicating only a suggested limit of ten members, as I described earlier (SCHWABER; SUTHERLAND, 2020).