Determine google map circle bounds offset, convert meters to coords (lat, lng), calc max zoom level to fit in map bounds

geo-coverter.js

//explanation https://en.wikipedia.org/wiki/Geographic_coordinate_system
const EARTH_RADIUS = 6378137;

const center = {
  lat: YOUR_CENTER_LATIDUTE,
  lng: YOUR_CENTER_LONGITUDE
};

const radianLat = YOUR_RADIUS_IN_METERS / EARTH_RADIUS;

const radianLng = radiusInMeters / (EARTH_RADIUS * Math.cos(Math.PI * center.lat / 180));

const offset0 = {
  lat: center.lat + radianLat * 180/Math.PI,
  lng: center.lng + radianLng * 180/Math.PI
};

const offset1 = {
  lat: center.lat - radianLat * 180/Math.PI,
  lng: center.lng - radianLng * 180/Math.PI
};

let angle = offset0.lng - offset1.lng;

if (angle < 0)
    angle += 360;

const GLOBE_WIDTH = 256; // a constant in Google's map projection

let zoom = Math.floor(Math.log((YOUR_MAP_OFFSET_WIDTH) * 360 / angle / GLOBE_WIDTH) / Math.LN2);