Smallest Pixel unit

HTML

<table>
    <tbody>
        <tr>
            <td width="30">a</td>
            <td>a</td>
            <td>a</td>
            <td>a</td>
            <td>a</td>
        </tr>
    </tbody>
</table>
<div id="output"></div>

<div id="int">a</div>
<div id="float">a</div>

CSS

table {
    /*width: 988px;*/
    padding:0;
    margin:0;
}
tr {
    /*width:100%;*/
    padding:0;
    margin:0;
}
td {
    width:20%;
    padding:0;
    margin:0;
}
#int {
    width:21px;
    background-color:red;
}
#float {
    width:21.4px;
    background-color:blue;
}

JavaScript

var tds = document.getElementsByTagName('td');


for (var td in tds) {
    if (tds[td].nodeType == 1) document.getElementById('output').innerHTML += parseFloat(tds[td].offsetWidth,10) + "px ";

}