The new Google Maps seems to use a diameter instead of a zoom value. You can use this function to get the old zoom value from the diameter. I tested it with the given list of values.

new_google_maps_zoom.js

function diameterToZoom (diameter) {
	var zoom = Math.floor(19 - Math.log(diameter / 1000) / Math.LN2);
	return zoom < 0 ? 0 : zoom > 20 ? 20 : zoom;
}

// tested with these values:
// diameter = zoom
//      758 = 19
//     1515 = 18
//     3031 = 17
//     6061 = 16
//    12122 = 15
//    24242 = 14
//    48480 = 13
//    96955 = 12
//   193999 = 11
//   388357 = 10
//   777642 =  9
//  1530533 =  8
//  3067439 =  7
//  7107071 =  6
// 12407563 =  5
// 27301053 =  4
// 51957442 =  3