Google maps range to zoom

Convert the Google maps range to zoom

HTML

<h2>Convert Google maps range to zoom</h2>
range: <input type="text" name="range"><br />
zoom: <input type="text" name="zoom" disabled>

JavaScript

$("input[name='range']").bind('input', function() { 
    range = parseFloat( $(this).val() );
    zoom=-(Math.log(range/591657550.500000)/Math.log(2))+1;
    $("input[name='zoom']").val( zoom.toFixed(6) );
})