<form> 

    <input type="file" onChange="getFileSize( this.value );">
    <img name="tempFile" id="tempFile" width="0" height="0"> 

    <br>
    <span id="sizeReport" style="color:red"></span>  Bytes

    <script language=javascript>
    function getFileSize( path )
    {
        var fileObj = document.getElementById("tempFile");
        fileObj.dynsrc = path;
        document.getElementById("sizeReport").innerText = fileObj.fileSize;
    }
    </script>

</form>