A world map comparison between Forza Horizon 5 and Forza Horizon 6 suggests that the latter is around 25% larger in scale.

Forza Horizon 5 hits 5M sales on PS5, providing yet another reason for Xbox to not return to console exclusives in the future
Bet it made more money on Playstation as well. Because Triple A, Gamepass, Day one, One dollar.
Today, Microsoft released another trailer showing off perhaps the most important location in Forza Horizon 6, the city of Tokyo.
Microsoft released another video focusing on the Japanese setting of Forza Horizon 6, focusing on the south-western island of Kyushu.
Mexico was already pretty massive. 25% bigger is a huge map!