<div id="container"></div>

#container {
    width: 300px;
    height: 300px;
    border: 1px solid red;
}

var cX = $('#container').offset().left + $('#container').width()/2;
var cY = $('#container').offset().top + $('#container').height()/2;

$(function(){
 var $this = $("#container");
 var offset = $this.offset();
 var width = $this.width();
 var height = $this.height();

 var centerX = offset.left + width / 2;
 var centerY = offset.top + height / 2;
 console.log(centerX ,centerY)

})

var div = $('#container');
var divCoords = {
    x : div.width() * 0.5 ,
    y : div.height() * 0.5
};