Код HTML:
<html><head>
<title></title>
</head>
<body>
<table border="1" height="50%" width="500">
<tr>
<td width="70%">
<table height="100%" id="myPage">
<tr><td>
LEFT
</td></tr></table>
</td>
<td width="30%">
<table height="100%" id="myColumn">
<tr><td>
RIGHT
</td>
</tr></table>
</td>
</tr>
</table>
<script>
aaa = (document.getElementById('myPage').offsetHeight);
document.getElementById('myColumn').innerHTML+="Height of page is "+""+aaa+""+"px");
</script>
</body></html>