Get WebMercator zoom level given a radius in miles

GetZoomFromRadius.js

function getZoomFromRadius(radius) {
  // Calculates the target zoom level given a radius in miles
 
  var mapDiv = $("#map");
  var mapWidth = mapDiv.width();
  var mapHeight = mapDiv.height();
 
  var radiusMeters = radius * 1609.34; // converting miles to meters
  var diameter = radiusMeters * 2;
  
  var basePixelSize = 156543.03392799936; // pixel size in meters at zoom level 0
  var pixelSize = Math.max((diameter / mapWidth), (diameter / mapHeight));
 
  var zoomFactor = 2; // default for tiled basemap
 
  var zoom = Math.log(basePixelSize / pixelSize) / Math.log(zoomFactor);
 
  return Math.round(zoom);
}