CSS
iframe { max-width: 100%; }
Javascript
function adjustIframes() { $('iframe').each(function() { var $this = $(this); var proportion = $this.data('proportion'); var width = $this.attr('width'); var actual_w = $this.width(); if (! proportion) { proportion = $this.attr('height') / width; $this.data('proportion', proportion); } if (actual_w != width) { $this.css('height', Math.round(actual_w * proportion) + 'px'); } }); } $(window).on('resize load', adjustIframes);