How to get the center of a polygon in google maps v3?

Algorithm:

Run through all the points in the polygon. For all the points find;

• x1, the lowest x coordinate
• y1, the lowest y coordinate
• x2, the highest x coordinate
• y2, the highest y coordinate

You now have the bounding rectangle, and can work out the center using:

center.x = x1 + ((x2 - x1) / 2);
center.y = y1 + ((y2 - y1) / 2);

Matthew's answer is a good solution. However, when using the Google Maps API v3, you might want to pass each point of the polygon to a LatLngBounds object through the extend() method, and then finally call the getCenter() method on the LatLngBounds object. Consider the following example:

var bounds = new google.maps.LatLngBounds();
var i;

// The Bermuda Triangle
var polygonCoords = [
  new google.maps.LatLng(25.774252, -80.190262),
  new google.maps.LatLng(18.466465, -66.118292),
  new google.maps.LatLng(32.321384, -64.757370),
  new google.maps.LatLng(25.774252, -80.190262)
];

for (i = 0; i < polygonCoords.length; i++) {
  bounds.extend(polygonCoords[i]);
}

// The Center of the Bermuda Triangle - (25.3939245, -72.473816)
console.log(bounds.getCenter());

Here is a custom function I wrote. Feel free to use it.

function polygonCenter(poly) {
    const vertices = poly.getPath();

    // put all latitudes and longitudes in arrays
    const longitudes = new Array(vertices.length).map((_, i) => vertices.getAt(i).lng());
    const latitudes = new Array(vertices.length).map((_, i) => vertices.getAt(i).lat());

    // sort the arrays low to high
    latitudes.sort();
    longitudes.sort();

    // get the min and max of each
    const lowX = latitudes[0];
    const highX = latitudes[latitudes.length - 1];
    const lowy = longitudes[0];
    const highy = longitudes[latitudes.length - 1];

    // center of the polygon is the starting point plus the midpoint
    const centerX = lowX + ((highX - lowX) / 2);
    const centerY = lowy + ((highy - lowy) / 2);

    return (new google.maps.LatLng(centerX, centerY));
}

you can extend the Polygon class with your own version of the missing function, let's call it my_getBounds() :

google.maps.Polygon.prototype.my_getBounds=function(){
    var bounds = new google.maps.LatLngBounds()
    this.getPath().forEach(function(element,index){bounds.extend(element)})
    return bounds
}

and than use it in code like this :

myPolygon.my_getBounds().getCenter()

... etc, it should be equivalent to the v2 behavior