COP30 in Belém registered 42,618 people on site and another 2,550 attending virtually, 45,168 in total.
Those are the official figures, published in December 2025. The number covers everyone with a badge: country delegations, UN bodies, intergovernmental organisations, admitted organisations, media, and the large support staff that runs the venue. It does not include the , which is not badged and which drew several hundred thousand visitors in Belém.
The size is worth holding in mind when you plan. A COP is not a conference you can see. With more than forty thousand people and dozens of pavilions each running six or seven sessions a day, everyone attends a different event. Choosing a narrow track before you arrive is the difference between a useful two weeks and a blur.