code: function getChartSize() {
  
  		containerWidth = (renderToClone || renderTo).offsetWidth;
  		containerHeight = (renderToClone || renderTo).offsetHeight;
  		chart.chartWidth = chartWidth = optionsChart.width || containerWidth || 600;
  		chart.chartHeight = chartHeight = optionsChart.height ||
  			// the offsetHeight of an empty container is 0 in standard browsers, but 19 in IE7:
  			(containerHeight > 19 ? containerHeight : 400);
  	}
docs: Get chart width and height according to options and container size