var spherical = google.maps.geometry.spherical,
    bounds = map.getBounds(),
    cor1 = bounds.getNorthEast(),
    cor2 = bounds.getSouthWest(),
    cor3 = new google.maps.LatLng(cor2.lat(), cor1.lng()),
    cor4 = new google.maps.LatLng(cor1.lat(), cor2.lng()),
    width = spherical.computeDistanceBetween(cor1,cor3),
    height = spherical.computeDistanceBetween( cor1, cor4);