what size for custom marker google maps code example

Example: google maps change size of marker

var marker = new google.maps.Marker({
 position: new google.maps.LatLng(data.latitude, data.longitude),
 map: map,
 icon: {
   url: marker_url,
   size: new google.maps.Size(36, 50),
   scaledSize: new google.maps.Size(36, 50),
   anchor: new google.maps.Point(0, 50)
  }
});