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

https://arthursuniquethoughts.publishlane.com/posts/how-much-room-do-i-need-to-roll-my-chair-back-safely

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