function calculate_area(){
  var t_length = parseFloat(document.area.input_length.value);
  var t_width = parseFloat(document.area.input_width.value);

  if ((t_length <= 0) || (isNaN(t_length))) {t_length = 1;}
  if ((t_width <= 0) || (isNaN(t_width))) {t_width = 1;}

  document.area.input_length.value = t_length;
  document.area.input_width.value = t_width;

  if (document.area.input_feet.checked){
	document.area.output_sq_feet.value = Math.round((t_length * t_width)*100)/100;
    document.area.output_sq_meters.value = Math.round(((t_length * t_width) * 0.09290304)*100)/100;
	document.area.output_tiles.value = Math.ceil((Math.ceil(t_length / 1.476378)) * (Math.ceil(t_width / 0.98425197)));
  } 
  else {
	document.area.output_sq_meters.value = Math.round((t_length * t_width)*100)/100;
    document.area.output_sq_feet.value = Math.round(((t_length * t_width) * 1/0.09290304)*100)/100;
	document.area.output_tiles.value = Math.ceil((Math.ceil(t_length / 0.45)) * (Math.ceil(t_width / 0.3)));
  }
}