var $win = $(window);
var $lay = $('#layout');
var baseSize = {
    w: 720,
    h: 500
}

function updateScale() {

    var ww = $win.width();
    var wh = $win.height();
    var newScale = 1;

    // compare ratios
    if(ww/wh < baseSize.w/baseSize.h) { // tall ratio
        newScale = ww / baseSize.w;
    } else { // wide ratio
        newScale = wh / baseSize.h;
    }

    $lay.css('transform', 'scale(' + newScale + ',' +  newScale + ')');

    console.log(newScale);
}

$(window).resize(updateScale);