[Octane]

В IE8+

var zoom = screen.deviceXDPI / screen.logicalXDPI;

https://github.com/yonran/detect-zoom
http://stackoverflow.com/questions/1...odern-browsers
http://stackoverflow.com/questions/9...-in-javascript
http://stackoverflow.com/questions/6...r-7-javascript
http://tests.novemberborn.net/browse...rcentages.html