A hardware math question

Hey,

I'm trying to figure out something about display sizes and in-game zoom.

There's two monitors; 24" 1080p and 27″ 1080p.

Game's zoom is set to 50 % for 24″ monitor. What zoom i need for 27 inch one if my goal is to have 1:1 ratio from same watching distance? Ie. if i have those two monitors set up side by side and watch a game i see everything same size, but more space with larger monitor.

Any thoughts? I also have same question for UI, but the zoom question is more important.