function BDWcalc ()
  {
    var listeners = document.getElementById('listeners').value;
    var bitrate = document.getElementById('bitrate').value;
    var hours = document.getElementById('hours').value;
    var days = document.getElementById('days').value;
    var total = document.getElementById('BDWTotal');
    
    var sum = days*hours*3600*bitrate/8*listeners/1024/1024;
    total.value = sum.toFixed(2)+" GB";
  }