Far smaller than the picture the trade press paints. The agencies you know are the exception: most Belgian agencies have fewer than ten people.
The measured figure
From the Agency Barometer, calculated on filed annual accounts: the median growing agency in the Belgian market had 7.1 full-time equivalents, the median shrinking one 7.8. Two numbers that are nearly identical, and that is the main finding: size does not predict growth. The rank correlation between headcount and growth is 0.003, which is zero.
Why that matters to you
An agency of seven can make excellent work and has little buffer. An agency of seventy has buffer and rarely puts its best people on a small client. Neither is better; they simply fail in different ways.
What size does tell you:
- Who will work on your account. At a small agency those are the people you met in the pitch. At a large one it depends on your budget relative to their other clients.
- What happens when someone leaves. At seven people you feel it, at seventy you do not.
- Whether they can absorb your peak. Ask how many people are on their busiest client right now and when that client's next campaign lands.
The dip in the middle
From the same measurement: agency profitability sags between roughly 5 and 40 full-time equivalents, with the deepest point between 15 and 40. Above 40 the EBITDA margin recovers to 17.1 percent and the share of loss-making agencies falls to 8.3 percent.
That is no reason to avoid an agency in that range. It is a reason to ask one more about its own plans: that group is under the most pressure to grow or merge, and that touches the continuity of your team.
See also: big agency or small and how big an agency really is.