function calculate() {
    var volume;
	var width = document.getElementById("width").value;
	var length = document.getElementById("length").value;
	var thickness = document.getElementById("thickness").value;
    if (document.getElementById("inch").checked) {
		thickness = thickness / 12;
	}
    
    volume = length * width * thickness / 27;
    document.getElementById("required").value = formatvalue(volume,7);
    return false;
}

function formatvalue(input, rsize) {
   var invalid = "**************************";
   var nines = "999999999999999999999999";
   var strin = "" + input;
   var fltin = parseFloat(strin);
   if (strin.indexOf("e") != -1 ||
       fltin > parseFloat(nines.substring(0,rsize)+".4")) {
      return invalid.substring(0, rsize);
   }  
   if (strin.length <= rsize) {return strin;}
   var rounded = "" + (fltin + (fltin - parseFloat(strin.substring(0, rsize))));
   return rounded.substring(0, rsize);
}