A 48x24-inch desk gives you enough space for a 27-inch monitor and room to move...

https://www.lima-bookmarkings.win/setting-up-a-cozy-gaming-space-starts-with-the-right-measurements-a-48x24-inch

A 48x24-inch desk gives you enough space for a 27-inch monitor and room to move your mouse comfortably. Leaving about 36 inches of clearance behind your chair ensures easy movement without feeling cramped