A 48x24-inch desk gives you enough room for a 27-inch monitor and your keyboard...

https://www.bookmarking-maze.win/setting-up-a-home-gaming-space-that-feels-just-right-starts-with-smart

A 48x24-inch desk gives you enough room for a 27-inch monitor and your keyboard without feeling cramped. Pair that with at least 36 inches of clearance behind your chair to move freely