goulet.js

//var size = jQuery('dt:contains("Size")').next().text();
//var count = jQuery('dt:contains("Sheet Count")').next().text();
//var price = jQuery('div.product-price span').text();

function paperSize(name)
{
    var cleanname = name.replace(/\W+/, '').toLowerCase();
    var m, alpha, i;

    if ( (m = cleanname.match(/^\s*([abc])(\d)\s*$/) ) ) {
        alpha = ({
            'a': 1.189207115002721,
            'b': 1.414213562373095,
            'c': 1.29683955465101})[m[1]];
        i = m[2];
        return (alpha * Math.pow(2, -(i+1)/2) * alpha * Math.pow(2, -i/2));
    }
    else {
        var others = {
            'letter': 0.216*0.279,
            'legal': 0.216*0.356,
            'tabloid': 0.279*0.432,
            'ledger': 0.432*0.279,
            'halfletter': 0.140*0.216,
            'juniorlegal': 0.127*0.203
        }

        if ( undefined !== others[cleanname] )
            return others[cleanname];
    }

    return null;
}

console.log(paperSize('A5'));