function calcMulch(el_feet, el_yards, el_lenght, el_width, el_height)
{
    var l = el_lenght.value * 12;
    var w = el_width.value * 12;
    var h = el_height.value;

    var v = l * w * h / 1728;

    el_feet.value = Math.round(v + 0.5);
    el_yards.value = Math.round((v / 27) + 0.5);
}

function validate(evt)
{
  var theEvent = evt || window.event;
  var key = theEvent.keyCode || theEvent.which;
  key = String.fromCharCode( key );
  var regex = /[0-9]|\./;
  if( !regex.test(key) ) {
    theEvent.returnValue = false;
    theEvent.preventDefault();
  }
}