Edit in JSFiddle

var maxHeight = 0;

$("div").each(function(){
   if ($(this).height() > maxHeight) { maxHeight = $(this).height(); }
});

$("div").height(maxHeight);

div{
    height:auto;
    width: 70px ;
    background:#eee;
    margin:3px;
    float:left;
}

<div>1<br />2<br />3<br />4<br />5</div>
<div>div</div>
<div>div</div>
<div>div</div>
<div></div>
<div>1<br />2<br />3<br />4<br />5<br />6<br />7<br />8<br />9</div>
<div></div>