สอบถามเรื่องการอัพโหลดโดยจำกัดขนาดของไฟล์ อย่างเช่นอยากจำกัดขนาด 700 MB ต่อครั้ง คิดเลขยังไงอ่ะคะ

<script>
function reset_file(name)
{
var elem=document.myform(name);
elem.parentNode.innerHTML=elem.parentNode.innerHTML;
return false;
}
function clickupload()
{
if(document.myform.fileupload.value.length==0)
{
alert("Please select file to upload");
return false;
}
alert("Now uploading please wait");
document.myform.btn.disabled=true;
return true;
}
function uploadok(pathfile)
{
document.myform.fileupload.style.display="none";
document.myform.btn.style.display="none";
document.myform.txt.style.display="";
document.myform.txt.value=pathfile;
alert("Upload complete\n"+pathfile);
return true;
}
function over_size(size)
{
alert("File not over 200 KB\n"+size+" KB");
reset_file("fileupload");
document.myform.btn.disabled=false;
return false;
}
function wrong_type(type)
{
alert("Please upload only file type\nGif, Jpg, Png, Pdf, Doc, Docx, Tiff\n"+type);
reset_file("fileupload");
document.myform.btn.disabled=false;
return false;
}
</script>
<iframe id="uploadtarget" name="uploadtarget" style="display=none"></iframe>
<form name="myform" action="upload.php" method="post" enctype="multipart/form-data" onsubmit="return clickupload();" target="uploadtarget">
<input name="fileupload" type="file"><br>
<font color="red" size="2">Not over 200 KB (Gif, Jpg, Pdf, Doc, Docx, Tiff)</font><br>
<input id="btn" name="btn" type="submit" value="Upload">
<input name="txt" style="display=none">&nbsp;
</form>

<?
$file = strtolower($_FILES["fileupload"]["name"]);
$sizefile = $_FILES["fileupload"]["size"]; 
$type= strrchr($file,".");
if($sizefile>204800)
 {
 ?>
<script>
window.parent.over_size("<?=$sizefile/1024?>");
</script>
<?
}
elseif(($type==".jpg")||($type==".jpeg")||($type==".gif")||($type==".png")||($type==".doc")||($type==".docx")||($type==".pdf")||($type==".tif")||($type==".tiff"))
{
$tempfile = date("Y-m-d")."-".$file;
copy($_FILES["fileupload"]["tmp_name"],$tempfile); 
?>
<script>
window.parent.uploadok("<?=$tempfile?>");
</script>
<?
}
else
{
?>
<script>
window.parent.wrong_type("<?=$_FILES["fileupload"]["name"]?>");
</script>
<?
}
?>