Easiest way to calculate area of drawn polygon with google map

Question

Javascript/google maps beginner here. I am looking for a simple way to calculate the area of a polygon the user draws on the map. Code Snippet:

function initMap() {
  var map = new google.maps.Map(document.getElementById('map'), {
    center: {
      lat: 53,
      lng: 0
    },
    zoom: 13
  });
  var drawingManager = new google.maps.drawing.DrawingManager({
    drawingMode: google.maps.drawing.OverlayType.MARKER,
    drawingControl: true,
    drawingControlOptions: {
      position: google.maps.ControlPosition.TOP_CENTER,
      drawingModes: ['polygon']
    },
    circleOptions: {
      fillColor: '#ffff00',
      fillOpacity: 1,
      strokeWeight: 5,
      clickable: false,
      editable: true,
      zIndex: 1
    }
  });
  drawingManager.setMap(map);
}

<div>
  <div id="map" style="width: 100%; height: 500px;"></div>
</div>

Answer 1

Use the google.maps.geometry.spherical.computeArea method

var infowindow = new google.maps.InfoWindow();
google.maps.event.addListener(drawingManager, 'polygoncomplete', function(polygon) {
  var area = google.maps.geometry.spherical.computeArea(polygon.getPath());
  infowindow.setContent("polygon area="+area.toFixed(2)+" sq meters");
  infowindow.setPosition(polygon.getPath().getAt(0));
  infowindow.open(map);
 });

proof of concept fiddle

code snippet:

function initMap() {
  var map = new google.maps.Map(document.getElementById('map'), {
    center: {
      lat: 53.000581,
      lng: -0.005
    },
    zoom: 19
  });
  var infowindow = new google.maps.InfoWindow();
  var polygon = new google.maps.Polygon({
    path: [{lat: 53.000842,lng: -0.004903},
           {lat: 53.000823,lng: -0.004798},
           {lat: 53.000779,lng: -0.004823},
           {lat: 53.000799,lng: -0.004935}],
    map: map
  });
  var area = google.maps.geometry.spherical.computeArea(polygon.getPath());

  infowindow.setContent("polygon area=" + area.toFixed(2) + " sq meters");
  infowindow.setPosition(polygon.getPath().getAt(0));
  infowindow.open(map);
  var drawingManager = new google.maps.drawing.DrawingManager({
    drawingMode: google.maps.drawing.OverlayType.MARKER,
    drawingControl: true,
    drawingControlOptions: {
      position: google.maps.ControlPosition.TOP_CENTER,
      drawingModes: ['polygon']
    },
    drawingMode: null
  });

  google.maps.event.addListener(drawingManager, 'polygoncomplete', function(polygon) {
    var area = google.maps.geometry.spherical.computeArea(polygon.getPath());
    infowindow.setContent("polygon area=" + area.toFixed(2) + " sq meters");
    infowindow.setPosition(polygon.getPath().getAt(0));
    infowindow.open(map);
  });
  drawingManager.setMap(map);
}
google.maps.event.addDomListener(window, "load", initMap);

html,
body,
#map {
  height: 100%;
  width: 100%;
  margin: 0px;
  padding: 0px
}

<script src="https://maps.googleapis.com/maps/api/js?libraries=geometry,drawing&key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>
<div id="map"></div>