Calculate google maps (or web mercator projection) zoom level resolutions.

calculate-google-maps-resolutions.js

var extent = {
  left: -20037508.342789244,
  right: 20037508.342789244,
  bottom: -20037508.342789244,
  top: 20037508.342789244
};
var size = 256; // map tile size
var resolutions = [];
for (var i=0; i< 24; i++) {
  resolutions.push( (extent.right - extent.left) / (256 * Math.pow(2,i)) );
}
console.log(resolutions);

//output of resolutions
/*
[ 156543.03392804097,
  78271.51696402048,
  39135.75848201024,
  19567.87924100512,
  9783.93962050256,
  4891.96981025128,
  2445.98490512564,
  1222.99245256282,
  611.49622628141,
  305.748113140705,
  152.8740565703525,
  76.43702828517625,
  38.21851414258813,
  19.109257071294063,
  9.554628535647032,
  4.777314267823516,
  2.388657133911758,
  1.194328566955879,
  0.5971642834779395,
  0.29858214173896974,
  0.14929107086948487,
  0.07464553543474244,
  0.03732276771737122,
  0.01866138385868561 ]
*/